In the great Indie v. Trad debate one thing that always comes up in the pro column for the Traditional Method is the author's advance. And really, who's going to argue about that? You get a publisher interested in your book, and then he gives you a pile of money. It's Yog's Law's perfect application.
Except... And of course you know there has to be an except...
First off, you don't get all that money at once. You get paid in installments, often three, one chunk when the project is accepted, one when you finish it, and one when it hits stores. This makes sense; the publisher wants to make sure he gets an actual book out of you. But at the same time, you're probably looking at a year or two before you've gotten all the money. Even a six figure advance doesn't look like all that much if you realize that's your entire income for the two years until your book hits the shelves and however long it takes to earn out the advance. Say you get a 200k advance, once you paid your taxes on it (almost 20% in FICA and Medicare alone, plus whatever federal, state, and local) and divide that by say (optimistically) four years. It's not exactly vast riches.
Secondly, that money is not just what you're living on, it's what you're using to promote your book. It's possible that if you're a big name, the publisher will set up book tours, speaking appearances, and the like for you. But if you're the kind of person reading this, you aren't that big of a name. If you're the kind of writer reading this and you want a book tour, you're paying for it out of that advance.
Thirdly, that advance is often all the money you're ever going to see from that book. An advance is supposedly your earnings paid to you before you earn them. A loan, really. Now, in most cases, somewhere in that contract will be something saying that if you don't earn out (your book doesn't sell enough copies to make you the advance) in a certain time (say three years) they own the book. What does that mean? It means that if you don't make back the advance, you never see any additional royalties on your work. Basically, your book is the collateral on that loan, and if it's not repaid in time, they get to keep it. So, say your book is earning a few hundred a month, not enough to have earned out your advance in the time allotted, but still it's a steady stream of income. Would you rather that money be going into your pocket or theirs?
Now, money in your hand now is worth more than potential money later on. But, when you're debating Indie or Trad, you need to go in with your eyes open and understand what those dollars really mean.