Supporting the assemblies that move on the robot is very important. Without planning proper supports, shafts may not be able to spin or actuators could be easily damaged.
Forces, or loads, that are at a right angle to the shaft are the most important forces to counteract. The floor pushing on a wheel or two gears pushing against each other are two examples of these forces.
It is best to support a shaft with two supports, one on each end. Without two supports, the shaft can pivot in the direction of the force. If, and only if, two supports are not possible, it is very important to minimize the distance between the force and the single support.