Ground life question

[IllGottenGain]

Ah, I meant to type lift in the title...hopefully people still know what I mean. I have a very quiet rig, due partly to my power conditioner and noise gate, plus my Epifani is also near silent. I have a question about the ground lift switch on the back of the amp. What does it really do? I know it's supposed to reduce 60 cycle hum, (which I don't really understand) but are there drawbacks from having it on?

[GrowlerBox]

If you have the DI connected to the soundboard during live use (for example), there may be a hum due to a ground loop. "Lifting the ground" can eliminate this. No magic or mystery. If you're not connected through the DI, it does nothing.