Actually, I think we're talking about 3 different options here.

One being that you can select in your Preferences to receive an email for any forum you wish to follow that way.

Two being that if you select a THREAD as a favorite, the link to it will display in your HOME PAGE area (pm/mailbox area) so you can direct click to it and not have to hunt it (them.)

Three being that you may select your favorite FORUMS and then toggle between seeing ALL the forums available or ONLY those in your Favorite listing. (Thus eliminating any that might, say, trigger you or that you never read etc.)