Important:
I figured out, that when you want to use these rigid groups on clothes, it is better to use the helpers geometry. Especially when you use these groups near the female breast region (I guess all other regions belonging to clothes far away from the body also). Here is an example, the buckle of the winter coat I recently uploaded:
Maybe you could add this picture to the tutorial and write one or two sentences, then it is perfect.
Btw.: sometimes errors occur, when you select the 3 points and start makeclothes. I normally try to select another point for at least one of the three points then and have another try.
I've no idea how it internally works, but I guess it is, that at least one dimension will create a zero value ... so that a calculation of resizing is not possible, but I could be wrong