Nothing at all. Differences in personal preference are as vast as the options available. For example: I don't write anything, but I sketch out interfaces and i

Nothing at all. Differences in personal preference are as vast as the options available. For example: I don't write anything, but I sketch out interfaces and ideas all the time, usually with a pen. Lots of people (my past (and maybe future?) self included) prefer pencils because they can be erased or just feel better in their hand/on paper.