Keep Additional bones is now "Optimize Game Objects"

So, I came across this and the help files haven't been updated yet.

I want to check this new option but I'm a little bit afraid that if I do check it, it's going to cause errors.

What happened to the "Keep additional bones" option? Is this to suggest that I'm going to have to scrap using the humanoid mecanim option in favour of the general option going forward?

 

The "Keep Additional Bones" has indeed disappeared and been replaced with the "Avatar Mask" located in the Animations import tab. You can basically say which bones should be affected by the animation clip. Just open the "Mask" section and check the relevant joints (or even better, create an avatar mask that you can simply reuse for all your animations).

That way you can keep using Humanoid rigs (and their benefits) while having numerous extra joints...