Mostly on higher difficulties. Just easier to let the trash take out the trash lol.

Neither did I, but I always take adventage of infighting to save stress on myself and to conserve ammunition in both UD and Dii... it was something I realy missed in Diii and RoE (please Zeni and ID, don't repeat the crapfest of RoE).

All the time. In Suburbs/Doom II for example (I think. It's been awhile.): I'd get them to start warping in, do a quick run around so they would start firing on one another, head for the other side of the map for a minute or two (a few would follow, but no biggie) and by the time I got back, I (usually) only had a handful of cacodemons and mancubi to deal with.