I've had to use it several times and every time it bumped a paying passenger. If you live in a place where there is a hub serviced primarily by RJ, your open flight is almost guaranteed to fill up after an inevitable delay by DCI. Plus, since most senior people wait until 1 hour prior to list for non-rev, the "what your seniority can hold 24 hours out" part only plays to my benefit to use UTC.

And this whole comment thread is about Endeavor. They have the same clause as we do. The major reason they were bumped up to S3A was because they are being bumped by retirees who could travel on any day and Endeavor was bumping paying pax on their backup. And that costs money.