The M/L toggles allow you to choose between momentary or latching behavior for each corresponding footswitch:
MOMENTARY A momentary switch is only engaged when it is held down. This can be useful for performance use, such as for capturing very short loops, enacting lightning fast pitch jumps, controlled glitches, or reversing part of a solo on the fly.
LATCHING A latching switch must be pressed once to engage, and once again to disengage. This is how most guitar pedal footswitches behave by default, and is typically useful for simple on/off functionality.