If you are talking about securing fittings then it's always a good idea to 'peg'them in as well to provide a mechanical fixing. Make a peg out of something suitable such as stiff wire and drill a hole in the bottom of the fitting. Glue the peg into the hole and drill a corresponding hole in the wood (deck?). Then you can check that the fitting is correctly positioned by dry fitting it before gluing into place.
Fittings which are simply glued into position are vulnerable to being knocked off by accident depending on how strong the joint is. A collision with another boat can result in expensive fittings going to the bottom of the pond!
Just belt and braces really.
Colin