Sometimes you need to add an extra protection to password-protected website. WP User plugin access to the login page can be restricted after N unsuccessful login attempts. This schema uses visitors IP address to store log attempts in the database and block access to login feature for N minutes (ex. 30 minutes) after N unsuccessful attempt.
There are a number of reasons to restrict access. One reason is security. Quite often users try to guess login and password combination to get unauthorised access to the system. Another reason is extra load on server.