[drol3]

In my mind it's surprisingly simple: you VERY honestly ask yourself the question of you know exactly what you are building. If you do then don't be afraid to plan ahead. If you don't, then ship the smallest thing that works :)

If you are doing a rewrite of an existing system or have many years of experience with a similar product then thinking ahead can save time. Otherwise you are probably better of not trying to be too clever.

The difficult part for most people is actually being honest in the process :)

Also Kent Becks timeless advice is good to keep in mind

1) make it work

2) make it right

3) make it fast

In that order. You might not need all three :)