ive always seen it as a rest.
ie one set of say 8 then a rest allowing u to push again for the 2nd 8 and so on
doing 24 in one hit will not allow you to use a lot of weight due to the tiring effect doing that much at once has.
so breaking it up into smaller chunks allows you to load the weight on, rather than tire yourself out in one hit
ive also always been told more weight less reps for strength, and less weight more reps for tone