I have a post Im working on that goes through the process of creating a Smush Mold. You have heard me talk of them before. Great for doing small detailed parts, but with a high err rate if you aren't careful.
Smush molds have what I call a Detraction Benefit. The Detraction being the design of the mold is such that resin gets in between the mold halves themselves resulting in extreme flash. If one takes to long to "Smush" or put the two halves together and the resin has already started to cure, you run the risk of having a cast piece thicker than planned. If the resin cures too much before putting the molds haves together it can really distort the cast to the point of being useless. But here is the Detraction Benefit. Casts have a 3%-5% Shrinkage Rate. So a 5 mm pin cast will be closer to 3/16" (.187") 5MM=.197" So it will be too loose for a standard 5 mm hole.
If I make the mold split down the middle of the 5 mm pin, I can at 180 Degrees apart have the pin slightly bigger than 5mm because of this extra "flash". With little sanding this can be brought back to a standard 5 mm fit @ 180 degrees. It wont be perfectly round but that's also another Benefit. You "Don't" want a perfectly round 5 mm peg. None of MEGO's pin are a perfect 5mm...you need room for the air to escape or the pin will always push back out when you try to put it in the hole. It wont seat properly. With a slightly oval pin this is accomplished.
So in this way, A Smush mold holds some benefit to a Sprue Mold. But it will come at the cost of some extra sanding.