Depends on the moment in the set, and also on the tune. If it's really the very start I'll play it through, and as I go further in the set, I'll mix faster and faster (it's not only the choice of tunes that defines the power of the mix, but also how you spin).
Also if I find the tune has enough energy in it from beginning to end, I'll more likely let it play.

But most of the time I think that isn't the case. I think there is a distinctive part in each tune where you can say : here's the energy. Once past that point, I think it's useless to continue playing the tune as is.

Of course it depends on the style also. I spin pretty energetic music so it's required to keep that energy high. On styles like house or progressive it's normal you keep things going for longer.

Alternatively of course, it could have been that the audience reacted badly to the track. If this is the case, he may have wanted to quickly move on to another track so as not to loose the audience.

For me it depends on genre as well as the other factors already mentioned.

When I spin hard trance I am more likely to use almost every inch of record as most have intresting outros which when mixed neatly with a good intro can create some mind blowing changes of pace and direction during a set which will always get a crowd going.

When I spin euphoric/light trance I never really go to the end of a tune. Best example I can use is Tiesto - Obsession where I very rarely let the track run into the main melody, bringing in a new tune after the first break. These tunes have such long outros that it is easy to pull off 2 minutes + in the mix!

depends...when i want to show off...ill go thru 35+ trackz an hour

if im in chill mode i'll only play about 18-20