Putting it in park, or longpress for (P) - what's the difference?

[JohnnyG]

Don't for get that newer cars don't have the parking brake caliper.

It was originally needed because the brakes were hydraulic only.

The brakes are still hydraulic. The "P" model cars still have the separate electric motor engaged parking brake calipers because they have the high performance 4 piston Brembo brake calipers. The non-"P" cars now have an integrated parking brake single piston rear caliper. This transition occurred approximately 10 months ago.

EDIT: New Rear Brake Calipers For non-Performance Model S and X