Groups as in "ad hoc" mini-communities that a user can elect to join (or can be invited to join by the group's moderator)?
Groups, as in, "usergroups" such that one's permissions to do things, and availability of features, is determined by the group(s) the user account is assigned to?
Dragonfly groups really serve as both of these. You can name a group "Awesome People" or whatever, invite people to join (or let them apply to join and then approve/deny them). You can add their group to the viewtopic so they feel like special snowflakes. The granularity of access you can decide to grant them is dependent on how the module was coded. In Forums for example, you can let each DF usergroup access or moderate each forum or not. But in say News, all you can really do is show or hide the whole module.
Coppermine has its own groups. All these are really good for is your latter description, i.e. managing permissions. You could use your Dragonfly groups to show or hide your entire Coppermine gallery, just like you can do with News. But if you want to manage permissions at the album level you must create and maintain a separate list of Coppermine groups.
What people are asking is that they want to not have to maintain two sets of groups and rather be able to manage Coppermine album level permissions with Dragonfly groups (or I assume that would be the logical way to go about it rather than the reverse as someone posted upthread).
I'm not so sure about that. Have you ever taken a good look at the cpg module? It is spaghetti tentacles reaching everywhere. I'm afraid to try to debug most of the issues with it. Debugging it is like Whack-A-Mole.
On the other hand, it's possible I'm making your point for you, and a simpler more elegant gallery could be written. But, there would almost certainly be some loss of features or integration, and, who will do it? Not me