This flips the sequence so the last line becomes first and the first becomes last.
Not the same as sorting
Reversing preserves the existing order and inverts it. Sorting imposes a new order. On an already-sorted list the two look similar; on unsorted data they are entirely different operations.
Where it is used
Chronological data exported oldest-first that you want newest-first, or checking the end of a long list without scrolling to it.
Reversing twice returns the original
The operation is its own inverse, which makes it safe to apply speculatively.
Try it: Reverse Line Order on SeoWolf's Notepad.