 Boosters were made in various configurations to suit different applications.In the days of direct current mains, voltage drop along the line was a problem so line boosters were used to correct it.Suppose that the mains voltage was 110 V. Houses near the power station would receive 110 volts but those remote from the power station might receive only 100 V so a line booster would be inserted at an appropriate point to "boost" the voltage.