I understand what they're trying to do with Fusion in regards to the Joints to cut down on having to define 3 mates to fully define a position, but I don't think that's functional. The joints work great when things line up just fine, but when trying to place things in an arbitrary spot in the middle of a plane, I've had nothing but problems. I used to use Solidworks a lot when I still had access to the eductional version to make a 3D assembly of woodworking projects before building them to make sure everything was going to fit. Using the mates, I could basically force a part to be in the position I wanted it, lets say X from one edge, Y from another, and flush on a 3rd side. I've been unable to figure out how to do that in Fusion.
In short, Joints are a good idea, but don't totally diregard mates or constraints to define rigid positions that don't line up with other edges. Something more precise than rigid group and move. Having both would be a great benefit instead of forcing people to just use joints.