My main amiga is rarely on for more than 5 minutes without either a C/C++ project going or octamed. My second 1200D is usually used for testing, retrogaming and also for running a midi translator tool I wrote (uses a file to remap midi program numbers, channels, drum note assignments, velocity curves etc in realtime).
The other 1200T (not actually mine, belongs to a friend) is mostly used for testing and the odd bit of coding.
Then there's UAE which is used for testing, large project compiling (a lot faster than doing it on a real 680x0 amiga) and the odd bit of retrogaming.