I always read that the more surfaces a part has, the more points of leakage there are. When using a physical gasket, it has two sides, both of which could be leak points. When using a form-in-place gasket, the RTV basically bonds the pan to the transmission so in effect it has zero sides and no leak points. Yes of course that assumes proper application. Yes you may want to let it drain overnight if fluid is leaking on the sealing surface. Yes in a shop where time is limited a gasket might be a better choice.Like Clinebarger said RTV is a cost cutting measure nothing more. Think about how the manufacturer applies the RTV, the unit is brand new and totally dry, the unit is upside down and a machine applies the RTV in a few seconds. It is easy and cheap, once the unit has fluid in it RTV is pretty much useless.
To the folks who refer to Blue Goo, Hylomar is not intended to replace a transmission pan gasket, it is fine for places that can use an anaerobic sealer and flanges and as a non hardening gasket sealer.