Depends on the game. In cases where I can fire during the reloading animation, like TF2, I usually reload whenever I'm not firing. Also, I make sure that the game doesn't count any ammo I have left as lost ammo, because I don't like to waste valuable bullets.
Also depends on clip size. Rocket launchers should be reloaded whenever possible.
Also depends on clip size. Rocket launchers should be reloaded whenever possible.