My initial hunch is that Brad is using what will eventually be Green's minutes in order to showcase guys like Rozier, Brown, Jerebko, Amir, and Zeller early in the season.
I could see us making a small trade with those guys and/or first round picks (plus Young and Mickey), or I could see us making a larger trade involving Bradley/Smart/Crowder. In either case Green would be a huge asset filling those leftover minutes (much better than Hunter at least).
His defensive rotations seem on, so I don't think that's why he was benched.
I have faith that Gerald can help this team. I think his dunks (along with Jaylen's) can give our team that spark/momentum we need to keep going and stop those scoring slumps.
I think a lineup with Smart, Green, Brown, Crowder/Bradley, and Horford/Kelly would be very long and tough defensively, while relentlessly aggressive offensively (as opposed to the passive pass around the perimeter and don't attack mentality the 2nd unit's been getting from Jerebko, Rozier, Amir, and Zeller).