Hi Nords.
Depending on MOS there is a permanent no travel list. My father has been retired for 20+ years and due to his unique MOS (technical), the militaries current use of old technology, and his clearance level he has to report any international travel to a pentagon retired asset management unit (?). [I don't know the exact title, I just know in his safety deposit box there is a phone number to call if he dies]. Since my father is the opposite of exotic and is old he has never been denied travel. He did get a visit from a consular officer and a couple of Marines in France one time--he told Pentagon he'd be gone 10 days, he changed his plans and stayed longer and forgot to update Pentagon.
I think this is really about tracking him when they need his help, and projecting how long it will take to collect him. Although I suppose there is some concern about coercion of information. Yes, they have come to his house and picked him up on multiple occasions, including 8 weeks following 9/11 (I only know because he makes them drop his pet off at my house).
Sorry if this is not a military explanation, it wasn't really an organization I wanted as an employer so I'm light on the specifics.