Is it best practice to leave the robot in auto mode or manual mode in idle for robot longevity?

There is a system parameter, Broke on time, which sets the time when idle for the brakes to be applied.
Find it in control panel → configuration → topics → motion → motion planner.
Read up on it in the technical manual System parameters.
It use to be the maximum allowed value by default, which is 3,600,000 seconds, 41 2/3 days!