In TortoiseHG 2.2 Workbench, I can right-click on the 'default' repository in the 'Repository Registry' pane, and click on the 'New Group' command. What does this New Group command do?
It looks like it simply is a way to reorganize your repositories into a tree structure instead of a flattened one, but I can't find any documentation on it, and I'm concerned that it might have side effects I don't know about.
The Repository Registry is merely a list of repositories that TortoiseHg keeps internally. You may have noticed that you can pull in repos from all over your hard drive, and they show up in a flat list under the default folder regardless of their actual directory location on your hard drive.
You can delete repos from this list or move them up and down in the list, and it doesn't affect the actual repo on the hard drive. Similary, if you create a folder in this Registry and move a repo into it, you're just rearranging this tree view, not changing anything in the actual repos.
Really, this is just a list/tree of shortcuts for opening repos in TortoiseHg Workbench, nothing more.
If you'd like to see where the Repository Registry actually exists, look here on Windows, or in the corresponding location in other OSes:
C:\Users\yourusername\AppData\Roaming\TortoiseHg\thg-reporegistry.xml