Case sensitive logins

Many users use Windows and in Windows, the most names are not case sensitive. So if you want a nice user experience you should avoid case sensitive names.

But Unix systems have used case sensitive names for 50 years with no problem at all, because their users had to know that smith, Smith and SMITH are 3 different names, either for files or for users.

If the names are given by an administrator, it does not matter whether they are or not case sensitive: no sane administrator would give smith to John Smith and Smith to Bob Evil. But when you have a system in which users can register automatically, it can be important to prevent Bob Evil to create a Smith account. If you don't, you would fail your professional duty of good practices and help Bob to impersonate John.