The 50psi is a maximum recommended for tire failure. They will have to run for a while at 50, but will fail early at that pressure.
32 to 35psi is the best range for on road comfort, tire longevity, tread life, and traction for the majority of tires and situations. Special situations for different pressures are high flotation off road (sand type surface, lower psi in most cases) and hard road heavy load (high weight, higher, but not usually to max psi).