I have only one pin (Rollergames) that has a center post between the flippers. I'd love to hear if the designers have added these as an afterthought when a game seems too unforgiving, or if they put them in from the beginning as part of the original design. This is more of a topic for conversation unless people have quotes or similar from a designer that has used them.
I forget that it's there, but it is pretty sweet when you "chill" and the ball bounces back into play.