To get the ball rolling:
I suspect that quail roos function somewhat similarly to chicken roos in the wild. They're there to fertilize eggs, protect the covey, and manage the hens. Quail are too small to fight predators, so a roo is only going to warn hens and/or get eaten instead - in the case of a human-kept covey, "protection" isn't meaningful. Thus, we're left with breeding/fertilization and social flock dynamics.
Note: all of my claims are from observing my own flock. It's a single flock kept in a semi-natural setting, in a cage off the ground with a ton of enrichment. They're honestly more pets than production animals, but we do cull or rehome birds that aren't good breeding prospects.
I've personally found that quail roo don't really get better with age - an aggressive male will not "mellow out." He might calm down a bit during winter, but he'll continue to be as aggressive as he was once spring hits. No amount or length of time outs has helped for us - and frankly, it seems like the roo is more frantic and pent-up after he's been let out of bad bird jail.
I've also found that there seems to be two routes to successful breeding with roos. All roos will try to breed, but some are more passive and aren't as likely to be successful - in this case I'm focusing on the more active breeders. Aggressive roos will chase a hen down and hold onto her feathers to prevent her from escaping, sometimes even plucking or scalping her if she runs or makes distress calls. Romantic roos will tidbit for the hens, who seem to then be more receptive to breeding attempts overall. I've noticed they rarely mate when tidbitting, but when they do mate they're more gentle and efficient - possibly because the hens are more receptive. For us humans, a romantic roo is probably preferable because it's very cute and also upsets the hens less.
And finally - I've noticed my most dominant new roo, Tiramisu, will try to manage the covey. I'm still not sure if he's actually trying to keep everyone in line, or if he just has a few favorite hens he's trying to protect, but when we're a bit late on refilling their dry food (they're also getting a fermented mash + treats) the covey gets riled up and birds will fight to get to the food. Tiramisu will make angry growling noises and occasionally peck at hens who are scuffling, and he does this until everyone has eaten and the covey is calming down.
Most of our males prior to our current two were aggressive about breeding but otherwise very passive within the flock. One was very passive all around. Our current boys are Tiramisu (more dominant but a good breeder and tidbits for the ladies) and Tidbit (more submissive but still a good breeder and loves to tidbit all the time). I'll probably never tolerate an aggressive male again - I just wasn't aware of the whole spectrum of male quail behavior and assumed that chasing and plucking were always normal.
WOW this blew my mind, I had no idea, how neat!!
