Besides from the already mentioned uses, I've seen 30 and 50 Amp single poles breakers used for larger computers or UPS loads. The UPS output can either be hard wired to devices or have eight to sixteen outlets on the back. (Four outlets per 20Amp breaker)
Typically they are in data centers and have been wired correctly but I've seen plenty of smaller shops chop of the twist-lock and install a 15Amp plug on the end.
