Hi,
Changing the brush size by leaning the pen (i.e. the more inclined the pen, the bigger the brush size) is a common feature in PAINTING software, which Photoshop lacks, and would be very welcomed by the painting crowd.
I've used a similar feature on Painter 11, MyPaint 1.0 and Gimp 2.8.6, and I find it really useful, since it allows a faster and less stressful access to a HIGHLY REPETITIVE TASK.
Thanks for your attention,
Antonio.