Magazine Springs
From what I have read, magazine springs don't take a "set" from being stored loaded (or unloaded). They only experience wear when they are actually used, i.e., when the magazine is loaded with rounds or is discharging rounds and the spring is being flexed or un-flexed. I cannot categorically state that this is the truth, but I've read it enough places to believe it. So it's a good idea not to use one magazine exclusively for shooting, but from what I have read it doesn't hurt to leave them loaded between shooting sessions. If other shooters have more accurate information on this point, I would welcome it.