We normally accomodate late sitting up until the end of the overture in musicals, or during the first break of a straight play. However, we recently did Beauty and the Beast, and sold out every show. It is printed on the tickets and signage in the lobby that if you do not pick up your unpaid, reserved ticket by show time, we have the right to sell your ticket to another patron. We had wait lists of up to 100 people one night, so we pushed that time to 5 minutes before the show. This was rarely a problem, thankfully, except for one night that really stood out in my mind. As front of house manager, I was responsible for filling seats and then turning away people we could fit. This night, however, we had a patron show up with his young daughter 45 minutes late to the show. He came to the box office where the ushers and I were waiting for intermission, and demanded that he be given his ticket and be seated. We tried to explain to him that his extreme tardiness unfortunately meant that his ticket was resold due to policy and that we can't seat anyone that late into the show. He proceed to become very angry with us, and told us that we were ruining his daughter's birthday.
What could you say? We have sign-age and tickets explaining our policy, but I feel that even if we had a billboard outside that said we will not seat you if you are late, this guy would have still argued with us. Signs are a great way to protect yourself, but seem to me utterly ineffective for the people it was meant for like Centuara was saying.