The numbers we are talking about control the % of the power that is set through the dip switches. So whatever your laser puts out is the 100% and 0% is off and ya go from there. 
EDIT: To elaborate, the laser power in GRBL is set by an SXXX code where XXX is a number for the power. How that number is interpreted depends on $30 Maximum Spindle Speed. The XXX is divided by the Maximum and multiplied by 100 to get the percent of power. So S500 with $30=1000 is 0.5 * 100 which equals 50% power and GRBL can then send the PWM signal for half power to the laser driver. That’s this laypersons understanding anyhow.