From b2evolution manual
This manual page is outdated. NEW PAGE: Blog All in b2evolution v5+.
The "Blog All" tab was relabeled "List" beginning in version 2.0, and blog aggregation took a new approach that does not involve a Blog All pre-installed page. See Blog List if you are using version 2.0 or higher.
 What is the "Blog All" blog?
"Blog All" is a special blog that is designed to show the admin every post that is posted in every single blog on your site. For example, if you have a blog called "Apple" and another separate blog called "Microsoft", the Blog All blog is going to take all the posts from both Apple and Microsoft and display them together.
Not only does Blog All aggregate normal blogs, it also will include posts to any linkblogs you use with your blogs (because a linkblog is really just a regular blog used for a special purpose).
 How can I use the "Blog All" blog?
The Blog All is great for pulling blog content together. For example, if you had a family website where each family member had their own blog you could visit the Blog All and get news on the whole family at once.
The Blog All can also be a useful tool for a site administrator with lots of users posting on lots of blogs. Since all the posts will show up in the Blog All it's an easy way to monitor the activity on your entire site.
The Blog All can be renamed and modified just like any other blog on your site. Just remember that it is the only blog with this special function.
 Can I delete the "Blog All" blog?
You cannot delete Blog All. It is the primary blog in the b2evolution database structure. You can "disable" it, however. Just make sure that no one has any 'write' access to Blog All.
- In the backoffice go to the Blogs tab, select Blog All and then the 'permissions' sub-tab.
- Disable all 'crosses' for everybody, so nobody will have any rights on Blog All.
- In the Blogs tab go to 'General' and uncheck the box to include Blog All in the bloglist.
 Can I exclude individual blogs from displaying on the "Blog All" blog?
b2evo posts are not linked to any specific blogs on your site. Instead they are tied to the specific category (or categories) you assign them to. So in order to keep a blog from displaying on the Blog All you would need to hide the specific categories which correspond to the blog you don't want showing up. Read this forum thread for more detailed instructions.
In future versions of b2evolution the Blog All will be greatly reduced in importance and you will not have to go to such great lengths to disable it.
 A common mistake with "Blog All."
"Blog All" is useful for many things, but it is not intended to be your primary production blog. One of the biggest errors new users make is choosing the "Blog All" as their default blog page. You can read more proper blog setup on the Sample/example blogs page or the Setup my blog page.