Angular 2 - Does subscribing to FormControl's valueChanges need an unsubscribe?

Below is a simple example of what I am asking about:

class AppComponent {

someInput: FormControl = new FormControl('');
private subscription: Subscription;

constructor(){

this.subscription = this.someInput.valueChanges
.subscribe(() => console.log("testing"));
}
}


I have 2 questions:

1) Do I have to eventually unsubscribe from this? 2) Most importantly, whatever the answer is to #1, WHY is that the answer?

Any insight would be appreciated!

Thanks!

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