User registration form and already registered

1. Why do you need user registration?
2. What does new user registration on WordPress mean?

Why do you need user registration?

Fraud prevention and data protection

Through the registration process, you can detect fraud and add a level of increased security to your program.

What does new user registration on WordPress mean?

The user activation feature helps you reduce spam user registration in WordPress. If you select the manual method, then all users must be approved by an admin before they can login to your site. If you select the email method, then the user must click on an activation link before they can login to your website.