Basically, useful only if you know how. Simply put technically it does work . . .. imaging you have an electronic finger that can pulse say 10 times per sec., and if your equipment (esc or GP brake servo) is responsive enough, then brake will be applied 10 times per sec (otherwise if equipment is not responsive, the effect will not be noticeable). As such esc/servo may get hotter and burnt out if overloaded. As to how useful it is ??? it will depend on your driving style, car setup and track condition etc etc. as other C-Hing have pointed out.
Hope this helps.
PS: some of you may have fast pulsating fingers perhaps . . .. ha ha