For his inevitable release.
If he has any value at all maybe they can carve out a late round pick. Like a classic AB 5th round pick instead of just cutting him. Any pick is better than 0. The value is higher if there are two teams in need of an experienced QB. I'm thinking due to injury but any two teams will work.
AB can extract a higher pick if he does a partial payment of his salary too, but the point is more value can be injected into what Watson is currently, which admittedly is pretty low at the moment.