I like to get mine in advance. Had a pain-in-the-... situation at Assen last summer. My wife dropped me off and I went to the window to pick up my tickets as per the Dorna email and there was no office there. Had to wait around for Dorna people to come pick me up and drive me to the accreditation office 15 miles away and waiting on line and schlepping back. Wasted a lot of time.
This year I got tickets through Pole Position and I had to bug them to send the tickets on time as promised and when they came there were no parking passes. I had to call a few times and they were saying Dorna only guarantee parking passes for every four people - which is not what I experienced at Assen. It was a given. I really didn't want to deal with waiting around for shuttles.