I actually find them useful on my old Nikons. I keep an MD-12 on one of my FEs, and I've found, alternating between using the motor drive and leaving it off, that I prefer shooting the F3 with the MD-4 attached, even if I'm not shooting fast. It just seems to balance better--the hand grip on the drive helps with that--and more comfortable overall to shoot that way. (And when I'm shooting film, really, I'm all about having fun.) I do take the motor drive off, of course, if I want to be stealthier/quieter/carrying more compact gear.
Practically, I've found that when I'm shooting some kinds of action--skateboarding and BMX in particular--that having the motor drive helps me sometimes get in a second or even third frame in an action sequence. I'm not shooting on continuous, but being able to keep the camera to my eye and carrying on with the focus--all of which is more difficult to do when advancing the film manually, you kind of have to break concentration to wind on (and avoid jabbing yourself in the eye with your thumb)--the drive enables me to grab another shot or two as things develop.
So, yeah--they had practical reasons when they were introduced with the cameras, and some of those are still valid today. But it *is* also cool sometimes to just slap the motor drive on your camera and get your old-school photojournalist vibe on! It's all about having fun.