Hi & thanks again for Ardour4 
speaking about subgroups, created with a right click on a group tab, is it ONLY a quicker way to {create a bus/goto audio connections window/change all the (e.g.) drums tracks output from master to this bus/route this bus to master or whatever} OR is it something I’ve missed in the possible uses of that feature ?
that’s all it is. you could set this all up as a series of manual steps if you (for some reason) preferred to do it that way.
A very good job, Sir Paul Thanks!
pretty much what it does, it groups your channels together and gives you the option to create a bus with the connections already done.
thers also parameter linking availble like fader mute etc.