When you are out of ammo for a craft weapon you get a message popup to let you know. However if the craft mounts multiple weapons of the same type you will get several identical messages in a row as the game tries to rearm each weapon in sequence. This quickly gets annoying because the message pauses the geoscape and in mods like xpiratez craft weapons are mostly found as random salvage, so it may be several months before you can loot more ammunition and make the popups go away.
The player doesn't need to see multiple messages of this kind because the first one already makes it obvious that you are out of 25mm cannon rounds or whatever. So the idea is that you could add a option to suppress duplicate craft reloading messages. The rules for this would be very simple, after a reload message is displayed any further messages for weapons mounted on the same craft that use the same ammunition type will not be shown.