Under no circumstances would I recommend buying a small contract in its own UY.
Agreed. It's not about having a contract on its own, that's not a problem, it's having a SMALL contract on its own is when you run into issues.
Having a small contract on its own means inevitably more transfers and you are much more likely to strand points than if it were with your other BCV contract.
For example, let's say you own 100 points at BCV in one use year and then you own a 25 point contract in another UY. The room you want costs 40 points a night and you're wanting 3 nights so 120 points.
You now either have to transfer 20 points over to the 100 pointer from the 25 point contract.
You could also borrow from the 15 points from the smaller contract to get up to the 40 needed for a night and then use 80 points to book 2 nights from the larger contract.
You could of course also borrow 20 from the larger contract to get to 120 but either way you're still borrowing.
Remember if you cancel, banking/borrowing and transfers are not reversible transactions. You must take a trip or rent out points for the UY you bank/borrow into. Compare this to if everything were in the same UY, everything would just return to the normal use year and no harm no foul assuming you cancelled before the holding deadline and weren't in the last few months of your use year. You wouldn't have to deal with transfers or calling member services to book your room or any of that.
Long story short, it's okay if the contract is large (IMO at least 100+ points) to have it on its own, but I would strongly advise against a small contract being by itself in a membership, especially when you already own points for that resort in another UY.