Reserved seating is better for families.
Another colleague, Noel Murray, one of the kindest individuals I know, likes assigned seating. So it pains me to have to gainsay him in public. He argues that he has a family of four, and for the whole clan to sit together it would mean coming to the theater super early to secure those spots.
My response is this: He's right. When you're right, you're right! If it's a hot ticket on a weekend evening, four seats together is going to be tough if you come too late. I say, let it happen! Some of my fondest early memories involve going to a movie theater of my youth (don't look for it now, it's turned into a gym) and waiting for the film to start. I remember my older sister torturing me, saying that we'd accidentally gone into the wrong auditorium, and any minute Wolfen or The Howling was about to start, and not The Great Muppet Caper.
I also remember there were times when it was too crowded for the four of us, and we'd pair off. I distinctly remember getting quality bonding time with my old man, playing Jotto as we waited for the start of Superman II and Krull. There were also times where my parents would let my sister and me sit together, and they'd have some alone time knowing we probably wouldn't kill one another during the movie. (I can still hear my sister telling me I was a loser for covering my eyes at the beginning of Raiders of the Lost Ark. "It's just like Gilligan's Island, all they're doing is running through a jungle!")