Rather than me explaining vacuum bagging Iíll excerpt this article (linked below). I expect that vacuum bagging is a separate entity from "oven cured epoxy". The purpose of this construction method is to reduce the amount of resin by squeezing it out of the uncured laminate.
"An ideal fiberglass layup minimizes the amount of resin because resin by itself adds weight without adding strength. When doing fiberglass layup by hand, it is hard to get the minimum amount of resin because you need enough to soak the cloth and the cloth doesn't lay completely flat against the surface. The solution to this is vacuum bagging."
"Vacuum bagging uses atmospheric pressure to press the cloth tightly against the surface being covered so that the excess resin is squeezed out and soaked up in a disposable outer wrap. This technique requires a vacuum bag, vacuum pump capable of pulling a significant vacuum (at least 25 inches of mercury) and various accessories and supplies. Thus vacuum bagging has been mostly restricted to large commercial use and a few enterprising hobbyists."
"Vacuum bagging requires that the part being laminated be covered with cloth (as in hand layups). The part is wrapped with a thin film which is porous and will not stick to the epoxy, called "release," and a thick layer of absorbent material, called "breather." This whole assembly is then inserted into the vacuum bag and the air inside is removed by a vacuum pump. Because the air inside the vacuum bag is removed, the air pressure from the atmosphere outside the bag pushes tightly from all sides, pressing the bag against the breather. The excess epoxy is squeezed out of the cloth, passes through the release and is soaked up by the breather. The breather also allows the air to flow away from the tube and out of the bag."
I expect this is a fairly costly construction technique for larger boats. Itís interesting to note this method has been used for some time for high quality touring kayaks (my kayak is constructed in this manner).