Even if I have to rebuild part (or all) of the application in some future moment, the initial productivity boost is worth a lot. Rebuilding a program that is already running is usually far less painful than building a fast one from scratch. At least the developers will have a test suite they can use to check whether their version is correct. And how much faster.

I agree there are cases where only the leanest and meanest code will do, but my point is that those cases are very rare.