I may be the one behind the times here but this surprised me when I learned it last night. (Edit: I am. It is a 5 month old feature). You can now allow Zoom participants to choose their own break out room.
Here is what setting that up looks like (you just have to check one box if you are already used to using break out rooms).
This is a long overdue feature that I can definitely see using in a number of ways. Two come to mind immediately. I can see this being useful at the end of a class to let students work together on different items. Or, if you are hosting a tutoring session you could have areas for quiet study and for collaboration.