Correct. In example, you've got your "logisitics" wing; in this context that's your healers. A commander ("logi-FC") within the channel issues orders to the sub-channel members, and no one outside the channel hears that. All members can still hear the parent channel.

In fights with 20-50 on each side particularly, it's really something to have the "pulse of the fight" because as a healer you can tell how well that's going.

A mumble server can be hosted with fairly low requirements if you're an org with less than 50 members in voice comms, and it's pretty embarrassing that a seemingly large majority of corporations can't even get 5 people into a call without an act of congress when gamers have tools like this so well explored.

The hierarchy can be set up to affect what people hear, and where they can speak. This is invaluable when you need to coordinate dozens or hundreds of players in real time. You can set up overlapping rooms where team leads hear their team member's voice chatter and their superior's voice chatter, and have the option of communicating in either direction. I usually had the two side buttons on my mouse set to push-to-talk, one that for talking up the hierarchy, one for talking downward. The exact setup everyone uses varies, but at minimum you can have a room for higher-level voice chat among team leads, while each lowest-level team is isolated to their own channel and can focus on the tasks given to them by their team lead. Mumble is also flexible enough that you don't need to strictly adhere to a hierarchy, you can have your lower-level players also be able to communicated laterally to groups of specialists who are handling specific support tasks.

This is all a difficult communication problem, but it's doubly difficult because decisions need to propagate up and down your communication hierarchy in seconds. Being able to manage this level of communication without it being a hopeless clusterfuck is a defining feature of effective organizations of players.