Currently, you can group layers by right clicking in the empty space/pane in the Layer Manager, then 'Layer Group' then 'New Group' or whatever is desired by the user. You can then start selecting what layers you want included in this new group. This in itself is a fairly useful function because you can right click in the same empty space/pane in the layer manager, and select group and it will highlight those layers you've added to that group.
To further this functionality, I believe it would be especially useful if that created 'Group' becomes an entity in the Layer Manager itself with some drop down functionality containing all layers that were selected to be in that group. This will reduce the clutter that could occur in the layer manager, but would also be efficient for the user. For example; the user could group all Road associated layers such as top of kerb, kerb channel etc. into a 'Road' group, and that 'Road' group is visible in the layer manager with a drop down arrow, showing all the layers that were added into this group.
Great Idea
Nice idea, maybe with the option to opt into this in program preferences.
So the option could say: Show groups in layer manager.