They never get to relax. MPs in garrison have it scummier than just about everyone else I know (going off just what I've seen in my time at Hood).
Its overseas where they get screwed the worse though. They get treated like infantry - have to do the same stuff in patrols, route clearing assistance, presence bs, but they don't get the same deliberate actioning that infantry does. If you 'think' you're gonna maybe need combat arms, you call the MPs. Which means that you're reactionary, probably not properly equipped, and your plan probably sucked to start with.
Just my 2 cents though.