The Lexus Control Arm is the suspension component on the front wheel assembly of your vehicle that controls the lateral movement of the wheel when the vehicle is in motion. This is possible since the control arm is connected not only to the frame of your Lexus but also the on the lower portion of the wheel assembly near the spindle.
The end of the Lexus control arm that is bolted to the frame will never be a concern to the owner unless the frame of the vehicle is rusted away or bent. The end of the control arm the Lexus owner has to not only be aware of but inspect on a regular basis is the end connected to the lower front wheel assembly. This end of the suspension component has a polymer grommet on it. This polymer will in time crack and break apart due to the stresses that are exerted upon it from the maneuvering of the vehicle. A worn grommet on the control arm end will cause the steering and maneuvering of the vehicle to be what is called sloppy or ill responsive to input from the driver.
When the condition of the grommet on your control arm warrants you to have this suspension component to be replaced, then it is recommended the one on the other side of the vehicle to also be replaced at the same time. The reason this is routine is due to the other suspension component has also had to endure the same level of stress and has the same time on your Lexus. Because of that it will be in the same condition or very close to it. If this advice is not adhered too, then the vehicle will be undergoing this same procedure very soon for the other side to correct the handling problems the driver is experiencing.