Your market may vary, but I can assure you that in Phoenix, you can drop the pin practically anywhere that's safe and legal.

The app has changed the method a few times. It used to show green or blue segments for valid spots, but today as it is, I just pick up the pin, drop it, hope for the best. It also demonstrates which way the car will be facing.

Dropping a precise pin on the map is no guarantee that it will actually stop right there, depending on the situation on the ground when it arrives. But, you can still adjust the pin while the car waits, or you can hit the "Pull Forward" button to try and improve it.

The app has also been updated to disallow adjustment of multiple dropoffs beyond the initial stop. So if you want a precise pin-drop in a multi-stop trip, you need to intervene along the way, instead of during your initial setup.

There was a recent case reported in the news, where people were trying to Waymo to the San Bruno airport, but their pin got dropped off in a residential neighborhood. This was apparently because Waymo doesn't directly serve the airport's lanes yet, so the pin dropped as close as possible, but the residents of that street were nonplussed about the results. So were the airline passengers who were lugging luggage!