Chothing in its natural position is almost always cut with arms down 45 degrees. If I would have say a jacket cur with arms in T-pose, I would be unable to lower my arms for the ball of fabric under my armpits. also, the fabric on my shoulders would be stretched to breakage.

Marvelous Desiger uses Arms lowered pose as a default, and all goes brilliant. If I want to fit my generated clothing with perfect flat and undistorted UV's to a T-Posed poser figure, disaster strikes. The sides of my jacket spread like wings.

I absolutely hate the default T-pose for this reason. 

I fully understand modeling arms and hands of base models is much easier in the T-pose. Textures however are much easier to make for the poses in which the skin is relaxed.

We need a tool to freeze a pose with all rotations etc applied as a new zero.