Suppose you were #48 on the torturous waitlist.
If Admissions just called in #47, would you make any decision or change anything you were doing versus if they had just called in #30?
The biggest decision I can think of having to make a commitment to another school. Even though applicants are able to hold multiple acceptances until April 15th, the schools might require a non-refundable deposit to hold your spot in class. In the worst case situation I can think of, Admissions is on #47, and you're 48, and the deadline for sending a $300 commitment deposit is today. I bet what most people would do is call Admissions and ask if they thought the waitlist is going to move. They have no idea.
Personally, I would take the sure thing and mail in the check on time and not assume movement of the waitlist late in the cycle. If you get in shortly after the check's mailed out, you could immediately place a stop order on the check.
Better to take action on a certain acceptance than on waitlist movement or near-acceptance. To each, his/her own.
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This reminds me of the time a friend returned home in the UA area to see a burglar run out. Stuff was stolen. Upon another friend's recommendation, she bought a gun. It sorta compensated for a feeling of loss of security, but how would having a gun in the original situation have helped her at all? The gun would have probably gotten stolen, too. It would have been better to start better habits of locking the door. Yes, it sucks to feel helpless and not in control of your situation, but...