I love using the Stopwatch and Timer apps while I'm cooking or brewing coffee, but I don't want their complications visible during the rest of the day. The ability to swipe left and bring up an entire watch face devoted to them and any other complications relevant to cooking is a game changer for me. I'll keep my existing primary watch face configured with the date, and a few activity / fitness complications, and I'll also have my Movie watch face with no distractions that Ryan Considine inspired me to use.
I hadn't even thought about using different watch faces for different tasks or themes of tasks.
I already switch faces of its the weekend (don't need calendar for example) but this will take it to a whole new level