Ball screw end bearings are responsible for holding the ball screw in place both axially and whatever it is that orthogonal-to-axially is called.

Overtightened ball screw end bearings will cause wear on the bearings and overheat the motor.

Undertightened ball screw end bearings will cause the screw to move around and not hold position well.

Do not tighten ball screw end bearings unless directed to by support.