Based info from DigWP.com we can have several configuration for WordPress Discussion setting based on how we want to handle comments and trackbacks (spam).
Loose: Comments and Trackbacks can come in with any moderation.
You should install several antispam plugin if you do not want your site/blog became spam destination.
Allow: Comments only from un-registered users but moderate all incoming comments.
You will be in pain if you don’t installed the right antispam plugin.
Moderate: Comments only and from registered users
You may not need antispam plugin, except if your wordpress version outdated
Disable: No Comments and Trackbacks are allowed.
You may not need antispam plugin, except if your wordpress version outdated
