The ability of the Toyota control arm to limit the lateral movement of the front wheel is really its only purpose. This is the suspension component that is attached to the frame of your Toyota and the bottom of the front wheel assembly. It will contain one or more polymer bushings that in time will wear out due to the stress and pressure being exerted on it requiring the control arm to be replaced.
When the bushings or polymer grommets wear out, the play in the movement the front wheel is then allowed to travel increase beyond the 1% a new control arm with fresh bushing could achieve. As the movement increases, the control over the front wheel by the driver decreases. This will be felt by the driver of the Toyota in the steering wheel when they are traveling straight down the road and when maneuvering.
The inspection of the Toyota control arms can only be accomplished with the vehicle lifted on a rack with the wheels suspended. During the inspection, the grommets should be looked at to see if there are any splitting or cracking in the polymer that has been caused by wear and stress on the control arm. This suspension component should also be grabbed by the inspector to see if it can be moved. If movement is noticed or cracks in the grommets can be seen, then replacement is warranted.
If a control arm on one side of your Toyota is worn and in need of replacing, then the one on the other side should also be replaced. Both suspension components have experienced the same level of stress and time on the vehicle and will be in similar shape.