You can never be absolutely certain what an autopilot in a single or light twin is going to do next! The A/P is useful to hold a heading, VOR radial or altitude while you review charts, or run a checklist, but you have to watch them like a hawk. I recently flew a PA28R, and on engaging George witha bugged heading set on the HSI, the aircraft entered a continuous right turn, with increasing angle of bank, and probably would have rolled inverted if I hadn't pressed the A/P disconnect button. Wish I could hire an aircraft where the A/P either works properly for more than one flight......or indeed, works at all!!