I think the Pin Control Group feature improves work flow but is limited by being pinned only in the sidebar. It would be much more useful if it can be pinned to the bottom of the Builder Canvas.
This improvement will greatly benefit the Custom CSS panel as you will have more space to view your CSS code and will not have to constantly expand the panel to full screen which covers the Canvas. This way you can write your CSS code and see the changes while you write them.
It also avoids blocking the settings of other control groups so you scroll less for panels that have a long list of settings.