Conventional wisdom to keep all your UYs the same is primarily aimed at being able to easily combine multiple contracts when booking, not having to juggle multiple banking deadlines, etc.
Every UY has those four "risky" months past the banking deadline. Overlapping two different UYs allows you to have points that are less at risk available during those "risky" months of the other contract, but it does come with some drawbacks as many have pointed out.
However, there's definitely some benefit to taking on the extra "hassle" of multiple UYs if you want to travel at all different times of the year and spread the UYs to provide coverage across the entire calendar.
For example, we have a SEP UY, which is great for all our possible travel dates except summer (which is past our banking deadline). We don't like to go in summer any more if we can help it, but there may be times when our kids/grandkids can only go then, so having that option without the banking risk could be attractive.
If/when we add on, we're now considering a different UY so the summer would be inside the banking window for that contract. The biggest downside, as I understand it, would be that, if we wanted to use points from both contracts for larger accommodations, we would have to book it as two separate reservations and put in a request to not move rooms (basically a split stay at the same resort?).
But that limitation can possibly be circumvented by transferring points from one contract to the other, right? If points are transferred, I know they retain their same home resort advantage (moot point if our contracts are both at the same resort). Do they also retain their UY/banking deadline? Thanks!