Not a question, but a side note: Wayne's jokes make this pretty dense-intense-tricky topic a lot easier to take in. In fact, my husband has been listening on the side while I watch this and bursted laughing on the Plot Twist 😅
He says your deliveries are impeccable Wayne! So thanks for entertaining the whole Tappan family on this side of the pond. 🙃🙃
ps. Just kidding, one question: you mention some good uses for this constraint but I can't picture any. The downsides seem to outweigh the upsides. Could you enlighten me on when this could be beneficial on animations?
Thank you for the kind words Nathi.
And you had your own plot twist there. (not a question > surprise question)
Excellent question too. But I'm not going to answer that!
.......Kidding.
Child of Constraints are used quite a lot with an animation technique called Space Switching.
This is where you constrain an object to a control, bake the animation, and then reverse the constraint.
You can then edit the animation on the object and bake it back to the control when you are done.
There are many situations where this is useful and is the fastest way to achieve the desired result
This sounds crazier than it actually is, but child of constraints are essential in many of the operations.
This probably has sparked a few more questions about "Space Switching", so if you want to learn more check out Pierrick Piccaut's work - P2Design. He has quite a lot of courses and videos on this technique.
Another use for the Child-of constraint, would be for simple dynamic parenting. It's kind of like the space switching technique but waaaaayyy less involved.
But I would only manually use the C-O constraint if you need to change parents one time (or less). If you are changing parents more than that, check out the add-on called "dynamic parent" - which automates all the steps in order to keep a handle on this hidden inverse matrix that comes along with the constraint.
I used to use multiple child of constraints for parent switching on some rigs when it was the only way I knew how, but the downside was that if you snapped you cursor to the selected control, it wouldn't actually snap the cursor to the correct position (as that operation didn't take the hidden matrix transformation into account)
There are 2 add-ons that can deal with this - one was made by Fin Eskimo called "Copy World Space" which can do 1 or 2 more useful things than the inbuilt add-on.
The other one is called "Global Space Copy" or something like that (I'm away from a real computer at the moment and this machine can't even open Blender....it's an old mac). But that one was made by Sybren and used to ship with Blender, but I'm pretty sure it's now an "extension" that you need too download.
Anyway, hope that helps.