Only for microfiber.
"Priming" the face of a foam pad for me only wastes product, and hastens saturation.
I usually start with four drops of product around the outside circumference of the pad, and reload with anywhere from one to three drops.
Of you look at how Rupes describes how to prime their pads, It's a similar approach to what I've done since day one with my PC. The dry foam eventually self primes during the initial set of section passes.
For the traditional orange and white foams, they seem to work better fully primed. I'm not a fan of those foams, so I don't often use them. The more open porous American foams, and closed cell European foams tend to work better with the dots.