How about "building" and "buiIding"? or "nodata" and "ｎodata"? You probably don't want people running around claiming to be admins because their name looks the same.

Similarly, do you really want to do tech support when someone forgets that their username is "nodata" instead of "Nodata", since their phone auto-capitalized things when they signed up? It happens. And how do you know they're "Nodata" and not "nOdata" or "nOdAtA"?