With regard to job utility outside of the service..... some agencies actually may give you credit for having served, but will use red pen due to having been an MP/SP/etc, because of the bad habits learned compared to "real" law enforcement.
Think about it: You're in an environment where everyone is basically respectful, knows that they're held by UCMJ. They know if they give law enforcement on base a hard time, that they don't only have to answer to repurcussions within UCMJ and the MP's, but also within their chain of command... so it's a double wammy. Generally speaking, you take your licks with regards to dealing with MP's. Backtalk, resisting, etc, while something MP's train to deal with, it's not something they GET to deal with and therefore really exercise verbal judo on de-escalation, bla de blah.
Due to this generally safe environment, complacency is bred... this complacency allows Ranger squads to come within arms reach of sleeping MP Specialists inside of their patrol cars, and scare the everliving shit out of them... Who said morning PT is always boring...
-----Edited to add some clarification-----
To further explain the "double whammy" concept, since you and others possibly reading don't understand law enforcement as it relates to those in the military... and mind you, this is pretty much second hand information as I kept my nose clean* and my minions of mass destruction feared what I am about to describe MORE than law enforcement's actions themselves...
@Teufel @Marauder06 feel free to chime in to correct anything.
When you are in the military, You're assigned to a unit. Regardless if you're the 153rd Field Sanitation Division or the 1st Black Ops Brigade, You have a commanding officer of some sort or another that owns your ass, figuratively. They have a "MP/SP/etc Blotter" they get from the post MP's. Anything any shitheads do, that they own, that results in any actual "Action" from on-post law enforcement....from getting a speeding ticket, driving without insurance, cracking a skull at the E-club, you name it on post, they are informed about. If you fuck up bad enough to actually get locked up, you aren't RELEASED until your chain of command comes and takes you.
So, what this means, is that your Chain of Command KNOWS if you fucked up. Fuck up bad enough, and you may have restrictions put in place upon your person. This whole ball of shit also rolls downhill and gains speed. Too many tickets? You may have your driving privileges revoked by your command. Too many issues while drinking? Direct lawful order to abstain from imbibing. Don't do as you're told there? Article 15's on top of your post-level shit you have to deal with. That means extra duty as assigned, reduction of rank, and forfeiture of a portion of your pay. Nevermind anything your NCO's may cook up if you're being a constant turd burglar.
This misbehavior also shows up when it comes to promotions, order of merit list stuff for schools, who's going to go on shit details, etc etc etc. Most people end up (rightfully) being more afraid of chain of command repercussions than anything that an MP could/would do to them.
* or just was smart enough to not get caught in the first fucking place, or knew the MP's, etc etc...