For commuting, I used to measure both rolling time and "wall clock" time. Beyond a certain point, reductions in rolling time no longer translated into significant reductions in wall clock time -- I just spent more time waiting at intersections. That didn't stop me from trying to get faster, though.

Now I don't measure anything, because my commute is so short that the numbers I collected would be more "noise" than "data". I save the measurements for my recreational rides.