Well, the RTV Silicone mold will break down, and eventually, after so many uses (depends on the quality, etc.) it'll start sticking to casts and tearing... My first mold I made was a POnda Baba head (few undercuts, nice and rounded, etc.). I probably pulled 50 casts from that mold in practice and after a while, a blue piece was here and there stuck to the casts... It was part of the inside of the mold.
The release agents are just something that helps the mold last longer... If you're pulling hundreds of casts, which you may be, it's useful to an extent...
The only thing I've used the vaseline/gasoline mix for is to keep halves of a 2-part mold from sticking together while making the mold... This is just a brief rundown of what I mean for those unsure...
-I make my mold box and fill the bottom with sculpey III, and with the head (or whatever) inside the clay HALF way.
-I fill the mold box, covering the OTHER half of the head that's exposed out of the clay, with Silicone... It cures.
-I remove the clay and turn the cured silicone half of the mold over into the mold box so it's now on the bottom... The exposed half of the head is facing up now instead of down before.
-I then put the THINNED gasoline/vaseline mixture over the top of the silicone (not the head, though it doesn't matter if it gets on there so long as it isn't thick and distorting the details of what I'm trying to cast).
-I pour more silicone in the mold box filling it up again.... It cures.
-I demold, and the gas/vas mix keeps the two halves from sticking. They separate perfectly... The head doesn't have to be "worked" out of the mold, so there's no risk of stretching the mold or losing detail there... It's pretty perfect, just more work, and generally used for parts with sharp undercuts and complex designs.