Assume that I have a goal of paying off the mortgage before full term (I know there are differing thoughts on whether this is a good financial move or not). And assume that I get a lump sum from a bonus or inheritance, or just the culmination of many months of additional paydown such that I've reduced the principal balance significantly.

If I wanted to improve my personal budget, I could possibly recast my mortgage and increase my monthly disposable income for other endeavors. And paying a small recast fee could be better than a full refi, with points, duplicate title insurance, and closing costs--assuming I'm OK keeping my current interest rate.