It puts me in control of the situation. As it is, an over-zealous prosecutor can get my ISP to comply. For personal systems, I assume that it would require an outright lawsuit/prosecution to force my hand to do anything. With competent representation, I assume it would need to be serious business and not a fishing expedition for them to get my email (should I comply at all).

And remember, passwords for crypto are still pretty much untested in (US) court. So far as I know, I currently cannot be forced to provide decryption passwords/keys for a court. Contempt might still be an issue, but that's another problem entirely.

Presumably the Fifth Amendment, which still protects one from disclosing their password unless the prosecutors have a witness who has seen illegal material on your device.

I imagine that it's easier to fight a subpoena directed at you than it is to fight one directed at Google (for example).