Monitors help the band hear itself and stay together. Get to the dance in plenty of time to do a sound check. Take time to get the monitor mix right first. Usually the caller is left out of the monitor so the band can focus on its sound. Have someone check the band balance in the hall, and the balance between the band and the caller.
Some callers like to shout into the mike.
This can overload the system and cause distortion of the whole sound. Also check as the dance progresses to see that the overall level has not been increased to the red line on the meter or LED's. Most systems have plenty of power and gain to fill the hall without overloading and distorting, but one must be sure no stage of the system is being overloaded.