What is the purpose of the session_regenerate_id() function?

The session_regenerate_id() function is primarily used to enhance the security of a user's session by generating a new session ID. This is particularly important in preventing session fixation attacks, where an attacker is able to hijack a user's session by exploiting a known session ID. By regenerating the session ID, it ensures that a newly generated ID replaces the old one, making it harder for an unauthorized party to gain access to the session data.

When a new session ID is created, the old session data is still accessible under the new ID for the current request, but it is essential to ensure that the old session ID is properly destroyed to maintain security. This function should be used at critical points in an application, such as after user authentication, to mitigate the risk of session hijacking effectively.

The other options do not accurately represent the key purpose of this function: enhancing security against session fixation rather than focusing on performance, deletion of sessions, or simply creating new sessions.