All eight channels can be set to whatever you want. Off the top of my head I think...

Sump Pump
Light -> type (for metal halides it waits like 20 min to try and turn them on after a power outage)
Powerhead -->wavemaker
Heater
Chiller

uhhh...that's all I can remember maybe some other things too. Just add up how many amps your going to be running, you may need the add on unit if it's over 15 amps.