This is truly a double-duty exercise. It serves two purposes. It builds explosiveness on the concentric (pulling) portion of a chin-up because each rep is re-set at the bottom of the movement.
It also takes you from single-chinner to multiple-chinner. This could be the result of increased grip strength and scapular retraction, which becomes a necessity since there's no need to swing, hump, or kip your way up.
Two of the hardest things about competing are sending in the entry fee for a competition and then not pulling out the last few weeks. Some of you don't compete and are just training for self-actualization, self-esteem, and to be healthier and more whole in your daily interactions in the journey we call a life experience.
Unfortunately, your old "what do ya wanna work today?" spur of the moment type training works a whole lot better than anything the Soviet Ministry Of Sport managed to cook up behind the Iron Curtain back in the 50's and 60's. Charles Staley explains why.