What's the difference between individual tracks and the combined backup?

Individual tracks are separate audio (and video) files for each participant, recorded locally on their device. These provide the best quality and flexibility for editing.

The combined backup is a single recording of everyone together, captured from the live call as a fallback. Because it comes from the live stream, its quality depends on everyone's connection. It's there as a safety net if an individual track didn't upload correctly, or if there's a sync problem.