Some of the most powerful features of BuddyPress relate to how it enhances your multisite network. Creating a network allows your members to start their own full-powered public or private WordPress blogs. Members can track new posts and comments from public blogs across the network of sites as they are posted in the sitewide activity stream, in the blog owner’s activity stream, and in the blogs directory page. These features help facilitate content discovery and social interaction on your network.
Note: When you are using multisite, and blog registration is enabled for users, there’ll be an option for “I want to create a blog” when registering.
When a blog selects “discourage search engines…” as a privacy setting, the blog won’t show up in activity directories, etc.