My band, a three piece rock/techno/metal band, only uses drums from a machine. We did initially use live recorded drums, but for the type of music we play, we needed the rhythm section to have exact precision, to tie in with stage effects or video, for some events.
So the entire rhythm section is generated within a DAW, using various tools, and synths and backing is added at this stage.
Then for our live shows, the guy who does drums and synth turns into our singer/rhythm guitarist.
This makes gigs, especially festival gigs which have a stage backline provided, very easy - we each turn up with a guitar and a rucksack - and that's it.
For some gigs we do add live drums, and we all use live drums in our other bands as we all agree they sound better in many situations, but it needs to be a specific reason for this band.
tl;dr - precision, matching video or visual effects, no desire to find drummers, ease of touring