If you are lucky enough to be accepted to Yale in the SCEA round, as much as you might want to immediately say yes, DON’T DO IT. There is absolutely no benefit in doing so, as you will not receive better classes, better dorm rooms or first pick of anything.
I highly recommend holding off on accepting Yale’s offer until your hear back from your other RD schools, especially if you need financial aid. Several of your RD schools might offer BETTER financial aid. If that happens, you can have Yale re-evalute your financial aid package given your other acceptance(s) from a peer school. If the other school’s aid is need-based and not merit-based, Yale might match the better offer.
If you accept Yale’s SCEA offer immediately, you will have lost your leverage in getting your financial aid increased because you foolishly said yes in December. DON’T DO IT!