It's simply a way to test and prove novel features. We have to test privacy improvements somehow, and we shouldn't be testing them on Bitcoin, as it is the main chain. The big daddy. Can't afford to make mistakes there. So we need other networks to test them on.
It's a falsehood to say that Bitcoin has reached a state of perfection and needs no more improvement. This is the complacency of many bitcoiners, and complacency kills.




