I literally save thousands a year with the Mosaic free same-day change and cancellation policies.
I rarely actually book the flight I need if I'm traveling alone. Instead, I'll book the cheapest flight for a city pair and then SDC to my desired flight (which often costs 2x-5x more than the flight I initially book).
Sometimes if I'm a few months out from a trip, and don't know which day I want to leave yet, I'll book one ticket for each day (let's say Thurs, Fri, Sat) while tickets are still cheap and then cancel the rest when I decide when I want to go.