It gives them the freedom to express their selves. Parents need to view the boards that their children frequent. Check to make sure the language and topics are appropriate. You need to instruct children not to post identifying information. There is safety in anonyminity.
Some services provide the opportunity to create a profile.
This is a great opportunity for a teen to tell everyone who they are, where they live, what activities they are involved in, and a lot of other information a predator would like to know. It is best to avoid profiles. Many services providers make web space available for members to create personal web pages. Kids enjoy doing web pages because it gives them a chance to be creative. Avoid personal information.