Server-side protection is more common because it allows you to control how many scripts a user can run at once. You can also use server-side protection to restrict the data a hand can access. For example, you could limit a script from accessing cookies or user data.
Both client-side and server-side protections have their benefits and drawbacks. Client-side protection is less secure because it leaves the browser open to attacks. Server-side protection is more secure, but it can be harder to use.
Why do websites need protection?