A current iPhone will be able to track your location 100% even without cell signal since it doesn't rely on cell for GPS function. I drove from Arizona to California through the Mojave desert and had tracking and way point reference the whole way.
1) I'm not convinced the built-in GPS units in modern cellphones and mobile devices are as capable as what you get in the dedicated standalone GPS units. I've used an iphone with a built-in GPS and I've used my Garmin Inreach quite extensively for off-the-grid navigation; my inreach generally is much better at getting and maintaining GPS signal, especially in mountainous and wooded terrain.
2) I recognize that most modern phones and mobile devices have the ability to give a location when out of cell range. My earlier post was pointing out that cell phones aren't as durable for outdoor or even in-car use (as earlier posts noted overheating issues). My iphone has overheated in the past as well, its vulnerable to moisture and it's batteries can drain very quickly in freezing temperatures. My inreach has been subjected to all kinds of abuse and weather, and I've never once had to worry about it breaking down.
If someone is planning on exploring really remote areas, either by foot or by vehicle, a dedicated GPS, at least as a backup, is a much safer bet than simply relying on an iphone or ipad...my 2 cents, but then again, I frequent areas in upstate NY where even a GPS unit doesn't always work and map/compass work is a required skill set.