It depends what you are driving.... Bashers for sure will not need it, large scalers and 1/8 offroad I also do not think they will notice it. But for sure 1/12 indoor and 1/8 circuit can have advantages of the speed. The latency in SR is shortened a lot and I think for a part it is with faster acting electronics within the servo, even when used in normal digital mode.

Funny thing is that most Sanwa drivers do use SSR/SXR servo's and most ESC's can work on those modes as well.

As mentioned Dario Balestri: