chrisb, I performed the same tests you did with the same results, nice write-up. In reference to using sketch attachment, I could live with an error popping up or a modeling halt but that isn't what I get, I get a contorted model that can really mess with your head to fix, often times when these breaks occur they mess up down stream features.
For comparison: The same model using re/deactivation.
With the plane deactivated, I removed a coincidence and the model threw an error as expected, with the coincidence replaced the model recomputed no problem.
I then added a cutout on the sketch and changed the angle, this of coarse did not compute correctly because the datum plane is deactivated. With a couple mouse clicks I do an automated or a manual face-datum plane reattachment. Everything is correct.
The big difference I see here is when changes need to be done and I'm in the midst of a complex model, I don't want sketches rotating or swapping sides, it just freaks me out.
I fixed many of those in the beginning and got pretty good at it but when you have a 100 hours into a customer model and it breaks somewhere back at it's beginning, well the blood pressure goes up for a while.
I found by using the deactivation method I get consistant results (when changing any sketch or feature) and I always let FreeCAD do the attachment so I know the dimensions and placements are correct. When topo errors are fixed then all datum planes can be activated.
I know everyone here has there own way of doing things and I can't change that (don't want to), but what about how do we teach the new users
. What do you think?