Just a recent example: tonight I decided to switch from unordered lists to checkboxes in my Bugs/FRs cards (to have visual cue when item is fixed). Search/Replace would allow me just to search for '* ’ in existing cards and replace it with '- [ ] '. Another similar example is here.
And, hey, this is all about text editing. Search/Replace is a must have tool for this: personally I often replace long names/titles with shortcuts for quick text entering, and then search/replace them all in one pass…