It is important to me on the modern day films and most of the Disney feature films but perhaps for different reasons than "Stereo" as a tag typically suggests.
It is not so much for effects zooming from left to right to match the actions up on the silver screen. Nor is it particularly important to me to even hear separation in a sound track "per-se" with film as with music.
No, it's for none of these reasons why I much much prefer my films that ought to be in stereo, to actually be in stereo.
It's because, what you gain by having two separate tracks and amplifiers outputting to two separate loudspeakers near to the corners of our silver screens, is a very important aspect of sound known as PRESENCE.
What this brings to the soundstage is a warmth and depth to the track that is otherwise missing by having a monoaural track or even by having the amalgamation of track one merged with track two.
It is a flat track and sounds like what it is... flat.
Just flick the switch on a decent Stereo recorded print from mono to stereo and the difference and improvements are crystal clear for all to hear!
It's the very same reason as to why, no matter how bad your singing voice is, it will always sound better in the bathroom than it ever could in a wide open space with no walls to bounce off.That is of course...unless you're Julie Andrews ha ha ha