If you rimshot a lot like me you have to...just a given, you hit, rim dips down a bit, lug has some wiggle room and yea, loosens itself ever so slowly. I know the head on my snare right now is probably 3 years old, love the sound of it though..lol, a worn out
yamaha head

Only area my snare loosens though is the 1/4 of the rim that faces me/where I rim shot.
Same thing happens to our marching snares at school, after a few performances I have to lightly tighten my batter head.