As I alluded to, I think it's different whether you're riding alone or in a group, and if in a group, what sort of a group.

In a paceline, I sometimes ride with people who get to the front and either accelerate or let their speed drop off. If they watched their speedo, they'd be able to maintain speed, and if they watched the timer, they'd figure out how long they could pull, and peel off before their speed starts to drop from fatigue.

On the evening rides, we've had an issue the last few weeks of people showing up who can't complete the distance before dark. Rides are posted in advance on mapmyride. If they knew their average speed over the terrain, they'd know to either plan a short cut or (sorry) just not come.