I use playlist groups for just two purposes:
1. Organisation
I have an "Audio" group which contains all audio related smart lists and playlists.
There's another of the same for images.
Then there's the MC managed "Recent Playing Nows" and pix01 groups.
on the root of the playlists tree, besides the default Recently Played and Top Hits lists, I have a "!Search Index!" smartlist that I use for quick searches not suited to the search bar and a "Played Today" smartlist that does just that.
Finally, I have a group there called "View Scheme Groups" which exists for the following reason:
2. Use in view schemes
It's possible to create a playlist group, add some smartlists and/or playlists to it, and then add that group as a pane in a view scheme.
Each playlist then shows as a selectable item in the pane.
The introduction of "Search List" panes in MC12 made this step redundant in many ways, but it does still have some useage value. The thing is, playlist groups created specifically for use in a view scheme will almost certainly never be visited directly, so I place them as inside this "View Scheme Groups" group to keep the tree tidy and uncluttered.
Now, other people that use MC to serve up playlists to external media players will probably use playlists and their groups in a much more serious way....
anyone?
marko.