[ksbrooksjr]

Well yeah obviously you can bypass the client code and directly connect to a server. That's not my point.

Client side validation doesn't prevent a malicious user from sending invalid requests, but it can prevent legitimate users from sending invalid data to your server accidentally. In fact, if I see validation failures showing up in my server logs for something I know should have been filtered out via client side validation, I can mark that ip address as being potentially malicious and rate-limit their future requests.

And as a user I would rather find out about validation issues immediately instead of waiting for a network round trip to the server. If I'm typing in a password for example and it doesn't meet the website's length/complexity requirements, I'd rather know as I'm typing instead of waiting for an HTTP request to complete. That extra HTTP request is wasting the user's bandwidth and the server's resources.