Same Apple ID on different devices

I use the same Apple ID on my iPhone and iMac and I don’t know if I should be doing that? It’s just leaving me more confused. I’ve connected my phone to backup photos and messages (which idk if it was necessary) thinking I’d clear more space. Once I’m done on the iMac do I need to sign out or “Remove from account” from my iPhone so the settings don’t affect my iPhone or does it need to stay on? I accidentally blocked someone and didn’t realize they were blocked from my phone also. So do I keep my iMac signed in? Also does using the same Apple ID on two devices require a lot of settings to be changed?