1.Analog to digital conversion plays a crucial role in the world we live in today. Most signals (e.g. a song or speech) are analog in nature. However, if you want to transmit them all over the world to multiple people at once, or if you want to enhance its quality by removing background noise, you will need to convert them into digital form.
2.In the isochronous speed control mode the speed will return to the original speed set point after a load has been applied or rejected. However in parallel operation this would cause instability as explained above.

In the droop speed control mode the speed will decrease by a fixed percentage when the generator is loaded from no-load to full load. This provides a stable working point for each load in case of parallel operation.
that's Why isochronous is better than synchronous.