I don't think I've actually turned mine off more than a half-dozen times since I got it. And four of those times were when I was on an airplane and had to power it down. Maybe that's bad, LOL.
I turn it off when I'm done with it for the day. Of course, it sometimes turns itself back on when the charger is plugged in.
I have actually only powered mine down maybe six times in the 3+ months I've had it. It's good to turn do the full power off every once in a while tom clear memory.....
I use to, but then I got my case and it got so very hot, then it was suggested to turn it completely off and charge it if in the case. So ~ I do and it doesn't get hot anymore.
Just as with a computer, there can be memory leaks in applications. Over time they fill up the ram and your device (smartphone, iPad....etc) may get sluggish or even lock up.... it's just a good idea to do a full power off (or re-set, actually the same thing). It is the same as doing a "re-boot" on a computer.... It just cleans things up nice on the inside It's one of those things I try to remember to do every few weeks or so.....
I have not turned mine off or restarted except for the rom update that came out. At night I use nightstand HD so it stays on almost all the time.