here again, busy with other things.
an important detail, the Motor6ds, and the rest of Welds, in animation are known as Joints. Joints are additional tools (implementation of a method or technique) that make the work much easier. Here it makes sense to talk about local transformation, because that’s what it’s all about.
In this case OP is asking about CFrames (if not, he would have just used Joint).
Exactly, you said it, it is a METHOD. very different from saying directly that it is local. When we want to be exact as OP wishes, of course.
I don’t really know what goes on behind the API, but I assume you have a reliable source for that. The problem with that information is that nothing can be done to take advantage of it. For example I would like to use quaternions directly to make some constraints simpler, like in Unity. But I only see CFrames. Another reason why it doesn’t matter is that a lot of other things can happen behind the API. For example an improvement of the hardwaare, more modern and better algorithms than a quaternion. So many other reasons why it could be better, but everything happens in a transparent way and there is no way to take advantage of that. A simple example: Cars come with manual or automatic transmission, everyone prefers the automatic because it is easier to drive with it. But others, like professional drivers, racers, prefer manual, because it allows them more control and they can make more efficient use of their car. In roblox there is only automatic.