During P.E., we are required to do the exercises that our coach scheduled for that day.
On average, we do about twenty jumping jacks, ten pushups and situps, and a bunch of stretches each day.
Yes, knee-pushups are useful if you don't have the initial strength to do full pushups.
Then apparently I do have the proper strength and just find it absolutely useless to do knee pushups. What I've been saying's apparently my opinion, then.