Because this is the guy who gets credit for saying it, that's why.
Ok, with the "why is there a picture of Ben Franklin in a post about being penny wise and pound foolish?" question out of the way, let's move on to the subject at hand, shall we?
Which is, well, being penny wise and pound foolish.
Here's a short story.
We're in the process of doing a small brochure on a project basis. We quoted a price that included preparation of some specific artwork, but this client wanted to spend a lot less, so we eliminated that - and other things - from the proposal to get to their price point.
Long story short, that artwork has become a colossal pain in the ass and has delayed production of the brochure by at least three weeks. The main reason for the delay is that the client isn't really equipped to deal with this sort of pain in the ass and is having issues properly preparing the artwork.
Of course, we are equipped to do it. And we coulda done it. Long ago. But it wasn't part of the deal and the client didn't want to pay the extra cost for us to do the work, Of course, if they'd accepted our original price in the first place, this artwork would have still been a pain in the ass, but it would have been our pain in the ass, not theirs.
So what should have been a simple brochure has become a problem and is way overdue. For no good reason.
My point here is that there is often a false economy when you Do It Yourself. Which is to say when you get a proposal from an agency or design firm and you want it done for less, think about whether or not you can really take up the slack for things you don't want to pay for.
Maybe it's a good idea to let people who know how to do certain things do those certain things.
Of course, I tend to think that if the most important factor in getting something done is how cheaply you can get it done (as opposed to, say, how well it can be done), then don't do it at all.
That's the cheapest way there is.