At the very least it tells the user they are using unsupported characters. So it's handy that way.
As far as actually doing anything more, not really.
It essentially filters what the server gets from the page's request methods (GET & POST). But that doesn't even matter because the server should always do some kind of sanitising of user input and never ever rely on client side for that.
That is btw what is happening here, the server sanitises what the user submitted, so the pattern for the text field is only serving a notification to the user when needed.
Unless something is broken, like bad escaping and misuse of white space and other encoding. Then it is no longer helpful and gets annoying and breaks the page in some way.
09-Sep-2016 16:13:33