Well, if your pistol is a 1911 the safety is for carrying it cocked and locked. If it's on then it's assumed that youve already loaded and readied the gun.

For bolt action rifles I read somewhere that it's to prevent the bolt coming open and possibly falling out of a slung rifle being carried through brush and the like. Also keeps crud out of the action by keeping it closed.

As above, though - I don't use safeties. Either the gun is loaded and about to be fired, or it is unloaded. If I'm in a situation where a gun must be rendered safe, the ammunition is removed and the action is unlocked.

If I hunted it would be the same - I'd rather the animal hear me racking the action and bolt, than carry a rifle with one up the spout. That did happen to me once, actually. boo hoo