In a long feature length film (over 120 minutes) intermission served a break for the audience. It served another purpose: for the projectionist to change the reel! Intermissions were often accompanied with the film's score - or a song score for a musical.
Many great epics had intermissions, as well as the Drive-in theaters. “Lawrence of Arabia”, “The Sound of Music”, even “It’s a Mad Mad Mad Mad World” had an intermission.
In today's theater going experience, the intermission seems to be from a by-gone era, as theater owners wish to show a film as many times as possible during the day. I would like to add a few pennies to the conversation and suggest that sweeping enormous epics that require an intermission shouldn't be shied away from. In fact, "Dances with Wolves" "Wolf of Wall Street" and even "Interstellar" could have benefited with an intermission. Not just for us poor audience members who were looking for a chance to stretch our legs, run to the restroom, but also to procure more popcorn for the bucket and soft drinks, also in bucket form. Of course, if a theater is going to offer free refills of concessions, the intermission doesn't help the bottom line.
But worth mentioning, if theater operators are concerned with audiences taking their movie consumption in living rooms, an intermission could give folks a familiar 'pause' - just like at home.