> When you normally start writing code first(typical TLD) then you need to have a plan before hand. This plan cannot change much because you really do not get feedback till you complete major segments of the code.

A good plan is modular and therefore flexible. I get lots of feedback as I'm writing the code. When I find myself writing very similar code over and over or an API feels unwieldy I take that feedback and refactor without delay.

I think what really happens in big groups of developers is that TDD forces everyone to delay agreement on the interfaces between code modules until the process of writing tests has uncovered most of the problems. With out TDD the devs who just want to get their part done and go home plow ahead with the first draft of the API locking it in stone before it's been vetted and then dig in their heels creating technical debt. TDD appears to be the saviour.