I have seen plenty of YouTube videos in which they use carbon fiber fabric to build various things. One such channel is Mike's Patey's channel where he makes amazing aircrafts from carbon fiber.
In these videos I usually see (but not always) that after they apply the resin to the fiber fabric, they put the structure in a kind of plastic bag and they vacuum pump it.
Why is that process? Is it hardening and giving some extra rigidity to the fiber in any way? Can this process be done by the use of pressure? (eg. a kind of mold that pressurizes the fiber from the outside so that the fiber also takes the correct shape).