Slipping to the inside

i found that i never really used it much in sparring. maybe its the thought that, as a southpaw if i slip inside an orthodox jab, i move right in the way of his right vice versa. i cant find a reason to want to make it work. someone convince me otherweise. i know im missing something.

You can ride his jab,since its mirroring you right in to his face

ah i see. so follow his jab on the way back and at the same time counter with my own left with the return motion of the slip.