I don't do a lot of borders. I mostly plan borders for when I need the quilt to be just that little bit wider/longer than the blocks take me. A sweet spot so to speak on the width and length, not too short, not too long.
I like to make my bed sized quilts to fit more like a bedspread. I can't stand 'blanket's' that pull up and barely cover your shoulders once you are in bed because it doesn't have enough width. I also like to have a quilt that I can put over my pillow, or fold it down some with the pillows on top, showing the back of the quilt.