On most wikis, it's not mandatory to have an account to edit or post comments. However, it is mandatory to have an account to go into the chatroom.
Having been a member of several different wikis, I've seen a few incidents that have led to very big problems. One particular incident was that a registered wiki user (who had various usernames, but was called John the Hacker by the people on the wiki) had managed to hack into several accounts and used them to spam.
If you decide to create a wikia account, here are a few tips to ensure that your account remains your own.
- Confirm your e-mail address. If someone does manage to hack your account, if you've confirmed your e-mail address, you can change your password. Which leads me to...
- Make sure your password is really, really good. You can use this website to find out how secure your password is.