What do you mean by "required"? There's different forms of string equality. It's plausible to have string equality that compares the actual codepoint sequence, vs string equality that compares NFC or NFD forms, and there's string equality that compares NFKC or NFKD forms. And heck, there's also comparing strings ignoring diacritics.

Any well-behaving software that's operating on user text should indeed do something other than just comparing the codepoints. In the case of searching a document, it's reasonable to do a diacritic-insensitive search, so if you search for "e" you could find "é" and "ê". But that's not true of all cases.

(OK, so "required" might be overstating it; you are perfectly free to write a program that doesn't conform to the standard. But most people will consider that a bug unless there is a good reason for it)

E.g. Norwegian had two common ways of collating æ,ø,å and their alternative forms ae, oe and aa. Phone books used to collate "ae" with æ, "oe" with ø and "aa" with å, while in other contexts "ae", "oe" and "aa" would often be collated based on their constituent parts. It's a lot less common these days for the pairs to be collated with æøå, but still not unheard of.

Of course it truly becomes entertaining to try to sort out when mixing in "foreign" characters. E.g I would be inclined to collate ö together with ø if collating predominantly Norwegian strings, since ö used to be fairly commonly used in Norway too, but these days you might also find it collated with "o".