If you are creating a blog where the members will come from different Local Authorities it is best to make it on the central /glowblogs instance.
The tile for this may not be visible on your dashboard but any glow user can access that instance directly at glowblogs and create or join blogs there.
The blogs authentication is currently tied to the LAs instance. That means if you need access to a glow only or private blog or to have a role on a blog in another Local Authority you will need the tile for that instance on your Unify Launchpad. Your school Unify administrator will be able to make that Tile available for you to your personal launch pad.
Here is a quick guide to Activating a Glow Blogs tile (pdf) for Unify Admins.