I interned at the US Embassy in Bern.

For a person of my age, it was the experience of a lifetime. While I was never bored, one of the less exciting parts was working in the administrative section, except the day I got to work with the travel manager to process vouchers.

I of course showered her with lots of questions about govīt travel policies (like when does the govīt buy you a biz class ticket). One involved miles. Quoth the travel manager:

Employees are encouraged to open a second mileage account and credit their govīt miles to it. If they deposit these miles to a personal account, they can be prosecuted. They cannot redeem the miles for personal travel, but when on official business can use them for upgrades and of course take advantage of any elite perks.

According to her, almost nobody at the embassy bothers to collect miles!