If you know where you are going, what value would you derive from having tests drive your development? Why wouldn't you want to be the driver?

TDD is most useful when you don't know what you are getting into. It allows you to quickly run small experiments against your hypotheses to see if the fuzzy thoughts running around your head are useful or need to be thrown out. The data gained from those experiments is what drives your development decisions.

If you already have everything already figured out, what more data do you need?