Automatic notification when sharing a project
When sharing a project, the member with whom you share it automatically receives a notification and possibly an email depending on the preferences setting of their account. So there is no need to send a buzz just to say to somebody that you have shared a project with him.
Buzz for more information
If you wish, you can send a Buzz from the project to notify one or more member(s) of the project to give them context or more information regarding this new project.
For more information, see the article on sending a Buzz.