When I've ordered tickets in advance it's almost always been for an IMAX showing. Getting to the nearest IMAX theatre is about two hours on public transit, give or take half an hour depending on making connections. And it's always a source of great anxiety for me, so I want to be sure of getting there in time and having my ticket confirmed.
There is a movie theatre much closer, but with no IMAX, half an hour away on foot or fifteen minutes by bus. But I still like to get there early to buy the ticket and pick the seat. Then I will go off to get a coffee and look in the shops, before coming back to the theatre about fifteen minutes before the showing.