When both surfaces are machined smooth and sufficiantly rigid for the clamping screws, no gasket is needed. For example some exhaust manifold to the heads.
Gaskets are intended for use as the gasket. Indianhead (shellac), High Tack, etc are only there to help position and hold them in place during assembly.
RTV gasket makers should generally be used alone - or in corners when the regular gasket won't fill.
