Ratings can be made for sexual content, political, personal, information, sports, coolness, boredom inducing, etc.
Can limit access to certain sites. I.e., school class can only open selected class related pages, no surfing.
Does not limit access unless software is set to limit access.
Can set to block any unrated sites, or sites not rated by a certain rating agency.
Can encrypt a rating services ratings to avoid alterations.
Can rate unwilling sites with the use of a rating service server.