It's not about reversing, but about checking whether reverse iteration works. This is required to perform proper truncation (for limited length fields) as well as visual editing for a cursor to go through the text.

It can additionally be an indication as to whether regular expression matching works, though that is usually handled by a library, and not the core string types.

My contention was always that if a "string" does not reverse text, then it's no better than an "array<char>". The existence of a "string" type implies it should do more.