Always buy-in for 100BB. And I think you have to be very solid preflop and postflop in order to play deep. Any mistake PF or on any street can be highly magnified when you're 200BB+ deep. Also, getting sticky with one pair
hands like TPTK or an overpair is not what you want to especially do deep. And stacking off with KK for 200+BB deep PF is probably a big mistake, but for 100BB is pretty standard.
Personally, I always go deep stack because I think I have an edge over the other players. Also, people seem to play way less back at you when you're 500BB+ deep. They tend to give up more on SB steals, c-betting, and just let you have it haha. I did lose 2 500BB pots recently, but I got it in as 82/18 and 90/10. Surprised that I didn't get one-outered for my first 500BB pot with the way I run sometimes haha.