You don't need any droop gauges or anything like a touring car. The best way to ensure it's equal is to measure how much of the shock shaft is visible between the shock body and top of the shock end.
For me, droop changes how much weight is transferred back and forth, on and off power. Also how much the car will lean left to right in the corners. I find less droop makes the car more stable, more droop make it's more lively/aggressive and sometimes more traction.
Droop also affects bump handling and landing. If the track is blown out and bumpy or has huge jumps then you will want more droop.