Originally Posted by
findark
If you have overlapping/impossible reservations, UA could randomly cancel the one you want to fly. You would cancel a BE ticket if you want to change it to something else on the same day -- you get no residual value from the BE ticket but now your record is clean.
This is what I was going to say. While the risk is low that they would cancel if you had another flight you decided you wanted to take a couple hours later, it’s there. And if you decided you wanted to say, take a first class seat on the same flight (lottery win? Inheritance?) you’d have no choice but to cancel your original ticket in order to rebook.
Point is there are legitimate reasons why someone would want to cancel a BE ticket and that’s why they allow you to.