As long as there's a split second, I always top myself off, thanks to accumulative ammo, else I'd be taking three shots, throwing out a 95% full clip. I like to be 100% prepared. I almost NEVER burn through a full clip, unless, you know it's the shitty assault rifles in fallout 3.
Although... I was one of those weirdos that spent the entire final mission of fallout 3 looting all the tesla armour and plasma guns, thinking I'd pick it up later