If you are trail riding with a group, you can be chatting one minute and the next minute the guys in front have started up and are away into the distance. If you haven't got a sidestand switch fitted, it isn't difficult to drive off with the stand down. All OK until the first LH corner when you get a nasty shock as the stand catches in the tarmac and throws the bike up in the air - been there, done that but survived. I always use a sidestand switch now.
Totally agree with Brian, side stand switch a must. I ride mainly in the bush and sometimes I'm preoccupied (and the old mind ain't that sharp) with a creek crossing , log jump etc so am thank full that I can't take off with the side stand down. Never been a problem.