Self registration has been disable. I've been getting several account created every day but no log-ins. I'm pretty sure this is from spam robots.

I've had to lock down all my sites because of these a-holes.

Anonymous users can do most things a casual visitor needs.

Unfortunately there are scum out there who want to spam anything they can.
I tried leaving the shoutbox and comment system open to all but had both spammed.

The main reason to register is to enable watches on pages you are interested in or to leave comments.

Clicking the watch (the eye symbol) on a page should result in notification being sent to your email address when the page is changed or a comment added. Obviously this can only happen if a valid email address is used.

Registered users can comment and use the shout box.

If you are planning to visit often it is worth registering and logging in so the wiki can tell you if anything has changed since your previous visit.

Currently only the admin can view the user list so your address is fairly safe. I have no interest in collecting addresses for shady purposes.
In future there may be extra admins and I can't run security checks on them.
I personally use disposable addresses when registering on sites like this.

Registering does not log you in. Register then log in.

About 30 percent of people who register don't ever log in - that is pretty pointless.
Users who never log in or don't log in for a year may be deleted.