ready
If a firearm has e.g. a seven round magazine, many people will load the magazine with seven rounds, insert it, and chamber a round, leaving the magazine with six. On many (but not all) firearms, it would then be possible to remove the magazine, insert another round, and re-insert the magazine. I've not studied the exact dimensions involved, but I believe inserting a fully-loaded magazine into a firearm whose action is closed will push down somewhat on the top round; a magazine which didn't have to allow that when fully loaded could be made a little shorter than one which did; not all magazines allow that, and consequently not all firearms can usefully hold "full magazine plus one".
Personally, I would tend to think that such loading would be a nuisance, since every time the weapon is cleared one would have a cartridge one would have to store somewhere other than the magazine, but I would not begrudge anyone who wanted to go through such effort in order to have a maximally-loaded weapon.