So here's a (semi-)hypothetical situation:

I'm travelling with my wife. We're both Marriott Rewards members.

Marriott is starting to run stay-based promotions, instead of nights-based. So, we decide that I'll check in the first night, check out in the morning, and then the next night check in under her name/MR number, etc. Rinse and repeat.

Well, the Regional Manager had a talk with the hotel manager about this, and it seems Marriott takes a dim view of this sort of shennanigans. So, rather than have them impound my points stash, we agree to not do that again.

Grrr. Now, only one promo per BigLar family, unless I want to send her off on a different itinerary, etc.