I really like the change for that reason. What I don't like is that when you open an old scene, all those checkboxes are checked so you have kind of destruction settings that you might not notice.

I have not noticed the progressive slowdown you're reporting (I'm not using a Mac though, maybe that's relevant?), even when I do multiple animations in the same scene. My #1 issue with animation is that I don't have a good way to insert frames between existing frames. Select and drag does not work right for all figures, some morphs do not carry over properly. Copy-paste does not work right if you have clothing that is set to auto scale to a figure that is not 100%, and in any case it's tedious if you just want to insert one frame in the middle. There might be a solution I'm overlooking but I haven't stumbled across it yet.