With iPhone 13 and an unlimited data plan should I leave cell data on all the time?

I have a limited sharing plan that my family uses and we leave cell data on all the time. I don’t think I’ve ever turned cell data off in 10 years of iPhone usage. Your phone uses cellular data if you’re not near a WiFi network that you can connect to. But since your plan is unlimited, you have no worries.

Yes. There's no reason to turn it off.