Can give greater confidence that an antenna system is installed correctly and without defects. Without measurements, this is difficult to know, as a sub optimum system will still function, but with reduced performance. SWR of the antenna and SWR of a complete system must be satisfactory.
Can quickly fault find defective antennas and associated feeder cable.
DTF feature will fault find cable.
SWR or return loss measurements on the antenna alone, will reveal faults with the antenna.