The vaseline is applied ONLY to the pinned type hinges. Robart hinge points have a metal pin in the plastic hinge pieces. CA hinges have no pin. (the pin is obvious in any that has it.... it will have segments to the hinge like a common household door hinge)

You are coating the places the "leaves" of the hinge mve against each other to prevent glue fom sticking in those areas. If you glue the pin to the leaves... then the hinge won't allw one leaf to move in relation to the other. That results in a control surface that won't move freely.

It doesn't take much vaseline... I apply it with a kid's watercolor brush. Don't get the vaseline on the portion of the hinge that is to be glued in the wood.. because then the glue won't stick properly.