I think the upshot is that if you're not doing something stupid then they're not going to bust you.

If I go up to Starbucks on a Sat night and buy a Frappichino and sit and bullshit with my friends, the police can't do shit about it. At that point I'm a customer of Starbucks, therefore I'm not trespassing.

Now when I leave, that opens me up to enforcement of Traffic laws....

THAT'S WHY YOU SHOULDN'T BE DOING STUPID SHIT LIKE BURNING OUT OR SHOWING OFF YOUR CRAPPY EXHAUST OR BOV. THAT'S WHAT ATTRACTS THE COPS....AND THAT'S WHEN YOU GET TICKETS FOR ALL THE ILLEGAL SHIT ON YOUR CAR