*If you’re carrying a longer-muzzled gun or a revolver, adding extra holster length may not be necessary for you, but for short semiautomatic guns, it’s often helpful.
Guns with short muzzles can be top-heavy and difficult to conceal comfortably. To solve this, some holsters have extra length added to the muzzle end. Like the keel on a boat, the extra muzzle length helps balance the holster, making it more comfortable and easier to conceal. This is especially true if you have a bit of a belly, which tends to push the grip out more and make the muzzle dig in.
Note that while extra muzzle length reduces grip printing, it can increase muzzle printing, which can be a concern with lower carry positions and tight fitting pants such as leggings or yoga pants.