While one person may want to boost with low drive using a loud pickup, while another may use single coils with the volume turned down. However the range of variation is still smaller than a main volume control, needing to go from very quiet to very loud smoothly. Usually an audio taper pot is used for that, while most dirt pedals use linear. As long as the volume works out to be more than about 1/4th, it is still less sensitive to adjust than audio taper, but it is very sensitive near off. With an (standard 10%) audio taper, most people will never use below halfway unless max. is super loud, while with linear it is the opposite.