The circuit as published is for phase control - as in dimming the lamp/heater or whatever. Note that phase control cannot be used to alter the speed of synchronous motors! You need to alter the frequency to do that. If you only want to switch the load on and off you need a zero crossing optocoupler that switches on or off at the mains zero crossing to keep interference low - the inductor is in the circuit for phase control applications and is unecessary for zero cross switching. If you use an optocoupler meant for phase control - you would want to synchronise the switching with the mains - this means extra circuitry and code.