Also it gives you greater precision if you are painting 'layer-by-layer', allowing you to make very slight changes each stroke
This is the problem with not having a graphics tablet, I wouldn't know what is normal. It makes sense that it gives you a finer degree of control, I was thinking more in terms of using a real pencil.
An optional behavior still sounds good but perhaps with relative pressure (as I understand it) being the default.
In addition a palette tool, where you can mix colors in a small window would be really nice :)
Do you have an example of one?