Deek
I tend to switch it off when I am no longer too busy doing other things.
This depends on weather, cabin status, attention level of the co-pilot, fatigue, ATC and the airport and general interest level that day
I like to maintain situational awareness and the autopilot is a useful tool to give me the extra capacity to keep a check as to whats going on.
There are also requirements to turn off the automatics on a non-precision approach when decending below the MDA.
Hope that helps.
