The "one big lump" theory of your money
Don't get confused by the way your money's divided up. It might be split up into IRAs, 401(k)s, 403(b)s, 529 plans, and annuities. Separately from that, it might be invested in different things--stocks, bonds, real estate, and cash. You might even use separate accounts to segregate your funds by goal--emergency fund, retirement savings, car down payment, and sending the kids to college. Despite all that, it's really one big lump of money.
All those things--compartments, investments, accounts--are tools. And it makes no more sense to treat your money as different because of the compartment it's in than it would to divide up your garden produce based on whether the plants were weeded with a hoe or a trowel.
Come to think of it, groceries make a pretty good metaphor. You divide your food up into categories several different ways--whether it needs to be refrigerated or not, whether it's home-grown or not, where it fits into the food pyramid (or four food groups, if you're old). But your goal is a healthful diet for your family, and you meet that goal with the smaller goals of a series of good meals. Your entire pantry is at your disposal to serve those goals, and you'd never assume that you can only make breakfast with foods in the refrigerator, while making dinner with only canned food.
When it comes to their money, though, people start thinking like that. They assume that the money in their retirement account has to be invested for their retirement. They mentally allocate specific investments to specific goals--so if the stock market goes one way they get a great vacation but can't afford to repave the driveway (or vice versa).
Don't do that. Instead, treat your money as one big lump that supports all your goals. Then, use the various compartments and investments and accounts as tools to help you use your one big lump of money to satisfy all your needs--and as many of your important wants as possible.
Let me pause here for a moment to say that I certainly understand the temptation to target some funds--I used to do that. I'd figure, if I just put $x out of each paycheck into some account, after so many months I'd have enough money to buy some thing or another. I used to wish for a facility that didn't exist then, but actually does now: sub-accounts. At most of the internet banks and brokerage firms, you can divide your account into sub-accounts targeted for some specific goal. Then, when you make a deposit, you can allocate the money among any or all of those sub-accounts.
It's really all in one account; they're just keeping track of a variety of subtotals for you. And that's one clue as to why it's better to treat your money as one big lump--because it really is.
There are several wins if you treat your money as one big lump.
One advantage is that some of your money can serve several purposes at once. This is most obviously true for cash.
You need cash for several purposes. You need cash for liquidity--to smooth out the fact that the dates that your bills are due on are not synchronized with the dates you get paid. You need cash for emergencies--because a certain category of problem can only be solved with ready cash that you can spend today. You also want to have cash on hand to take advantage of opportunities--tomato paste going on sale is not an emergency, but there are huge investment returns (tax free!) if you stock up when you see a great deal. You also sometimes need to accumulate a large sum of cash for large transactions like a car purchase or a real estate closing.
To a considerable extent, you can use one pool of cash to support all these purposes. The money you keep on hand for liquidity is part of your emergency fund. You don't want to tie up a large fraction of your emergency fund in "opportunities," but you can invest several percent of it in household staples without putting your finances at risk (in fact, for a certain category of emergencies, such as a flood or a blizzard, a few jars of peanut butter and a big bag of rice is a lot more useful than cash in an internet savings account).
The same is true of all the other categories of investments in your portfolio. All your stock investments support all your long-term goals. All your bond investments support all your medium-term goals. And so on.
Another big advantage to treating your money as one big lump is that it's a more accurate model of reality.
If you're one of the people who puts a few dollars every paycheck into several different accounts, each saving up for some particular goal, what happens if there's an emergency? You've got two choices: You either cover your emergency with credit (and pay interest), or else you raid your special purpose accounts for the cash (and feel bad).
You have the same two choices if you treat your money as one big lump--except that you can skip the feeling bad part, because you never pretended that the money was "allocated" to some goal or another. It was all part of your one big lump of money that supports all your goals--including dealing with an emergency.
Divided the money up by goal is one of those little tricks people use to fool themselves into doing the saving that they want to do, to keep themselves from just spending it on passing whims. Although I'm generally in favor of whatever tricks people find that seem to work for them, I think this one should be avoided.
See, what you're doing is lying to yourself. If you're only lying to yourself about the little things--pretending you only have the money in your checking account to get by until payday--that's fine. But your entire portfolio is too important for you to be managing it with one eye closed, pretending that it's something other than what it is.
If you've got a plan for satisfying your wants, you've already got all the advantages of pre-allocating the money, without the disadvantages of lying to yourself.
Just like the person who puts money into a bunch of separate accounts, figure out how much you need to save to fund all your various goals--and then save that much. But instead of dividing the money into separate accounts based on goal, feed it all into your one big lump of money--and then manage that one big lump of money as a unified portfolio that supports all your goals.
Optimize compartment advantages
Finally, once you're managing your money as one big lump, you're in a much better position to take maximum advantage of things like tax-advantaged accounts such as IRAs and 401(k)s.
See, income earned in those accounts accumulates tax-free, but any money that you take out of those accounts is taxed as income--including capital gains that would otherwise have been taxed at a favored rate. So, the key to take advantage is to use those compartments to hold income-earning securities. Don't fund your IRA or 401(k) with long-term investments for your retirement! Fund your IRA or 401(k) with things that earn interest. (I wrote about this in more detail in Your 401(k) is not an investment.)
If you think that your 401(k) or IRA needs to have a balanced retirement portfolio, you're going to miss out on some of the juicy tax advantages that the plans offer. The key to avoiding that misstep is to understand that your whole portfolio is one big lump of your money. No individual account or compartment needs to be balanced on its own--it's only your entire portfolio that needs to be balanced.
And the way to keep that perspective is to treat your money as one big lump that supports all your goals.