Some opamps pull a lot of unexpected supply current if they are railed. I'm doing a thing with an OPA171, nice little amp, but I'm using a wimpy shunt regulator to make a -3 supply, and was concerned if the amps might bog it down.
Turns out that it uses about 450 uA at 10 volts supply, and pulls
*less* current as it rails in either direction. That's good news.
It also comes off the rails cleanly in a few uS, so it could make a decent comparator.