Just to expand on Doc's comments, with separate Use Years the contracts exist as stand alone entities. You cannot easily combine points for a single reservation...not like when you have the same Use Year. Right now the only way to combine them is with a phone call to Member Services. So you'll need to prepare for those phone calls and make sure you don't get yourself into a pinch when trying to make a 7/11 month reservation. Online reservations start at 8am but MS doesn't open until 9am. You could end up at least an hour behind other folks trying to book.
Right now
DVC does not enforce the "one transfer per year" limit when there is shared ownership but I guess it's a possibility that philosophy that could change. I doubt they will ever change those rules but in the interest of full disclosure, it's worth mentioning.
In GoofyLo's case, I suspect the separate logons are necessary because the contracts are titled differently. If you want everything merged together you need to make sure the contracts have
exactly the same ownership.
And obviously you'll have to monitor separate banking deadlines.
Personally I think it's a lot easier to add points in the same Use Year. Add up all of these annoyances and separate Use Years will create some headaches over the next 40-50 years. To an active, seasoned owner it's probably easy to stay on top of everything. But if it's just a case of waiting a few more weeks for a similar contract to appear with the same UY--or paying a couple dollars more per point--personally I'd go that route. All it takes is one lost reservation or forgotten banking deadline to make the wait worthwhile.
YMMV.