I think Pixar will do low-resolution runs all through the day (so people can get immediate feedback on what they are doing), and a high resolution run overnight

I think Pixar will do low-resolution runs all through the day (so people can get immediate feedback on what they are doing), and a high resolution run overnight (so they can see the current product). If you're at close to 100% utilisation, and have a large cluster, renting hardware is very cost inefficient.