I sometimes flat SC's against regs that steal a lot but give up too often postflop as they can continue on more flops than say 44. Also 3 bet them occasionally.

Against people who play very fit or fold leading flops with draws/air can be profitable because they fold so much of their range.

Obviously setmine against 8/7 types.

Depends on the player mostly but you won't go wrong by playing tight in the blinds - position is so important in NLHE that you should be trying to defend the button and play hands in position much more than defending the SB/BB.