I havent read all replies, but heres my input.
I got my Powered Rack in February. I use my Kemper for practicing at home (through a 2x12 Zilla cab) and playing live (through a JCM800 4x12 cab).
At first i struggled to find a tone/profiles i was happy with - due to having too much choice and always thinking there was something better. Or just adjusting the profiles too much from the factory setting, trying to turn them into something else.
I bought my Kemper 2nd hand and the lad before me had hundreds of profiles on it. What i did was take all profiles off the Kemper except the factory one, and keep them in Rig Manager.
I then downloaded some free packs from Michael Britt, Tone Junkie,Top Jimi, Thre Amp Factory etc. From this i decided i like the sound of Michael Britt and Tone Junkie profiles. I bought a couple of packs and set about picking my favourites - the ones most useful to me.
From there i tried and tested a few profiles at home, rehearsals and live, and finally settled on a handful of maybe 6 or 7 that i really like and i can use properly (for gigging). I'll use 2 or 3 at a time in my performance and then sometimes swap some out for the other favorites just for a nice change.
I still like to try out other profiles when practicing at home, but its more a case of pick one and play rather than pick one and faff around all night. Every now-and-then ill favorite a new one and add it into the cycle for gig profiles above.
One thing i did find out is its better, in my opinion, to not alter the profiles too much (e.g. mid, bass, gain, treble, clarity, definition etc. etc.). I pick the ones that sound about right out of the box, and if needs be (depending on room or stage) ill just adjust the overall Monitor or Main output EQs to suit each gig.