Lets get this set straight. Resin should never be exposed to a vacuum. By resin I mean any of the stuff that is mixed 50/50, has the consistency of thin syrup and becomes either white or tan when cured. The reason for this is the liquid becomes very volatile in a vacuum and certain chemicals become gaseous in this low-pressure environment-- in other words, accelerated outgassing. This is what causes the resin to foam up, not the tiny amount of air trapped in the mold. When normal air pressure is restored, the resin appears to be back to normal. Depending on the volume of the part, a lot or a little damage has been done to the material due to the outgassing and the part may or may not cure properly. It could become extremely brittle. It could weep polyol at some point down the line. It could also be perfectly fine, but the point is, the alternative (pressure or talcum powder) is much better.
Epoxy is different from resin. Way different, chemically; and due to its viscocity, using a vacuum to get rid of bubbles in epoxy is the only way to go. The difference between the two problems is that resin traps small amounts of air against the mold when it is poured; epoxy captures a rather large volume of air within the body of the material as it is mixed-- and some against the mold. It also has a much slower cure rate, which allows time to properly deair the part before the cure starts. As hobbiests, these are the facts of life. There are commercial resin compounds that allow for vacuum deairing, but we don't use those. They have been formulated for use in much fancier equipment than we have the budget or the need for.
One last comment-- someone mentioned making RTV molds using a pressure system. The only reason this is a bad idea is it is possible any trapped air will simply be compressed during the cure and when the mold is exposed to normal air pressure the air in the bubble will want to expand. If this is anywhere near the surface used to create the part, it is possible that the surface will distort, resulting in an inward bulge in the part. The same thing occurs in molds that are not deaired at all, but in reverse. The bubbles trapped near the surface of the rubber of the mold heat up and swell during repeated use and can also cause small dimples in the part.
I hate when that happens!