Well, this padding is useful only because we display a blue background when hovering. Before, it was padding: 4px; but @ssrihari changed that to padding-left: 0px in https://github.com/diaspora/diaspora/pull/4445 because he wanted the menu to be aligned with the profile picture. I find the blue background weird to have a space all around but not at left, so this "hack" restore the left padding but keep the menu aligned with the profile picture with the negative margin.