I haven’t used a case since the 5S and have upgraded every year since then. I’ve shattered (yes the entire display was cracked, no information could be seen whatsoever) one display, but the cases I’ve used in the past wouldn’t have stopped the damage that did happen. I just find cases annoying since they often make the phone significantly bulkier. I’d probably get used to using a case, but I currently prefer the feel of using it without a case. I also had a bit of trouble getting a nonbranded, solid-colored case for cheap, so it just wasn’t worth it paying for it imo.
I have noticed more searches and dents in the devices I haven’t had a case on, but these don’t matter to me as they don’t change the functionality of the device. With that said, you’ll likely get less resale value if your phone isn’t in top condition. Being in the iPhone upgrade program means I don’t have to worry about resale and can freely use the device how I want it, without feeling guilty for decreasing the value