Fusion
Grounding locks the origin (not the geometry) of the grounded component to the top level origin in that design.
If an assembly with one, or more grounded parts is inserted into another assembly, now the previously founded parts in that assembly are floating.
That is where many people get confused.
Rigid grouping a component also locks the origin of the involved components together. If that involves the top level origin in a design than the effect is the same as grounding.
The difference is that this relationship is maintained when that assembly is inserted into another design.
The advantage of grounding is that it removes the grounded component(s) from the joint solver calculations so in assemblies with many moving parts this can make a significant performance difference.
I left this comment on the youtube video above:
The video explains a symptom but does not explain the reason for it. I've been trying to explain this many times in the Fusion 360 forum. Watch your Origins! I guess as I invented Fusion 360's R.U.L.E.#1 & 2 that might be a worthy R.U.L.E #3 ? The reason the grounded assembly is floating is because Aaron used a rigid as-built joint. The rigid as-built joint and the rigid group joint do not require selection of a reference (joint origin) on a component, so they can only use the origin of that component. The grounded assembly references the top level origin but when it is inserted into the assembly the ground reference is nil. If he had used a rigid joint or revolute etc. basically any joint that requires a user to select geometry to place a joint origin on then the grounded assembly would have also worked fine. While I also prefer the rigid group or as-built rigid joint method, the "Ground" command has one advantage in that it removes components from the joint solver calculations. In complex assemblies that can make quite a difference
Adding into this thread is perfect as it provides the canvas for my explanation.
Thanks to @Aaron.Magnin for making one of his super smooth recordings!
