When lowering the front suspension the bump stops will remain in the same position! This means that if you hit a bump or ramp hard the suspension will travel a lot less before hitting the bump stops. Thus preventing the suspension to fully absorb the bump and sending a heavy thud throughput the car – not really doing it any good.
The bump stops can be quite easily adjusted by removing it with the spacer and refitting with the spacer (cut in half) fitted at the top
When the suspension on the rear is lowered on a rubber bumper mgb then you need to fit the shorter chrome binder bumper axle straps to prevent the axle dropping too far.