The US government used to bar employees from earning miles for personal use from US govt business flights. Also, there are some startups out there that have a similar policy where award tickets are to be returned to the company for use as corporate travel.

I used to work for a company that let me keep my miles, but made me fly on AAdvantage awards for some business flights. It wasn't that bad because I could add stopovers for my own personal use on these tix. Just hated the fact that I had to ride in the back and could earn qualifying miles.

The one cool part was that I could buy paid upgrades to F/J and not have to wait for the upgrade window. I'm glad I work for a large corporate now and can earn as much as I want.