The thing is, you rarely do much data transfer at a gig. You do it right, all you have is the HD being read, not written to. That's usually not a problem if you have a brown out, spike, whatever... But WRITING to a disk can have much more catastrophic consequences if interrupted.

Unless you use a long pre-load for a sampler, I wouldn't go as far as to say a UPS should be de rigeur on live gigs. But it doesn't HURT to have one. I've got one for a couple of gigs where I'll end up on a long cord sharing power with the PA, or I'm outside with a good chance of local thunder

But home, it's 100% UPS. That's where I do all my backups, registration creation and data transfer. Living in Florida means accepting that, at any time, the power can go out, flicker, whatever. When you live in the lightning capitol of the States, having a UPS is pretty much mandatory..!