While I can understand singularly every blend mode of the paintbrush from the math point of view, I cannot find a use for most of them (the only ones I used are for drawing a castle and these were "Color,Value,Saturation").
So I'd like to know how do you use/used blend modes (of the paintbrush! I'm NOT interested in blending layers) to paint your pictures in GIMP.
Please avoid "this take 50% of the color from channel blah" answers (I understand the math).
I'd like answers that are (possibily short) sentences that explain the goal and why that blend mode was right for that task. If it is also possible showing a small piece of image before and after application of the paintbrush and the shape of the paintbrush that would be an additional point!
(Photoshop answers counts as long as the same blending mode exist in GIMP, I'll check everything and if works the same.).
Saturation: I wanted to grey-en certain parts of the image, the saturation mode allowed to do that. This is cool if you exagerate with color, or if you want to make more vivid certain part of the images by increasing the saturation.
Value: I wanted to brighten-darken certain parts of the image to adjust highlights or shadows.
EDIT: To be more precise, I don't want answers like "Pencil is used to change color of pixels along a path to foreground color in selected layer". If the answer end up in saying "this math operation is applied to pixels" than it is usefull to noone and anyway would just be a copy of what GIMP documentation already says.
A more usefull answer is "Pencil is used to draw lines".