Know how to turn them on and off. A straight line can accidentally end up being several end-to-end segments which "endpoints" will show you. Endpoints will show intersections of very slight angles that you wouldn't otherwise notice and help you see polygons that you didn't know where there. It will help you see why some surface shapes defy closing as you draw line after line.

I get my sketchyphysics "thing" working and the whole program crashes. Then I re-open the file only to find that all my toolbar settings have to be reconfigured to the way I like them... again and again and again... Frustrating! How do I prevent this?

Looking for a way to stop an SP simulation and then use that position as the new starting position. Example would be letting an object fall and settle to a resting point then saving that as the starting point when the simulation resets.