Text search, text replacement, ellipsizing text at the end or middle (as done commonly on iOS), fuzzy search, password word limits, password length limits, matching passwords (try using bcrypt on international languages without first normalizing), detecting and filtering rude words in public chat, ... Basically anywhere that text needs to be checked or changed.
Just off the top of my head. There are far more. You can't even have a native language user friendly login system without normalizing text.
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