First of all, you don't do a 25 mph course at 20 mph. That's a terrible speed for a 25mile tt, for a racer trying to do TT's anyway.

Second, 1.5-2 minutes over a 25 mile course is a HUGE savings when placings are determined by a few seconds.

If you're just goofing around on them, then yeah it won't matter, but if you're racing and the time actually counts, then they're a good thing to have...