I don't know where this habit is coming from. Anybody got a clue?
Piston singles where throttles can vibrate towards closed.
If you want to monitor the autothrottle just put a couple of fingers behind the levers at pedestal level, that way the other guy doesn't constantly worry that you're overpowering the system. The only time I can think of when the autothrottle function is so critical it needs hands on is during a coupled approach. Seems clumsily OTT on climbout.
What about the FO's who, even when you are PF (and often in the cruise) still hang onto the control column?
I guess it is a bit like smoking as a way to so something with an unoccupied hand.
Sometimes it feels as if there are too many unoccupied hands on a modern flight deck and some people just haven't learned to sit on them...