The As-Built Joint tool lets you define the relative motion between components without repositioning them in Fusion.
Use this tool when the components are already positioned relative to each other in an assembly. As-built joints are particularly useful if you're using imported components or you're taken a top-down design approach to assembly modeling, since the component don't need to be moved.
Unlike the Joint command, since the As-Built Joint command doesn't reposition the components, either of the components you select can be grounded.