Using both feet makes it much easier to execute a continuous legato pedal line. It also contributes towards increased rhythmic control when playing either in a legato style or in the less legato lines commonly used in performing older music.
Avoid the tendency to draw an imaginary line near the center of the pedal board, and then to play all keys to the left of the line with the left foot, and those to the right with the right foot. Instead, learn to pivot freely, using the right foot to help in the lower range, and the left foot in the upper range of the pedalboard.