This is a different version than the first Lower Weapon mod that came out shortly following the release of Fallout 4. This mod adds increased time delay and checks for certain actions before raising/lowering your weapon.
If you're someone who has never held a weapon for a long time, you might not know that you're only ever pointing your weapon forward (or at your target for generally as long as you're firing in that direction). Guns are heavy blokes and your arms wouldn't be able to maintain a "fire-ready" position for long. So this makes things a lot more realistic.