John, If you ever need to get a remote start, most systems require a third key be placed under the dash in a special module....
I like a spare non chipped key i carry in my wallet.... I use it when i need to open he tanou cover and don't have my keys, OR the tailgate...
Yes you can use the door code....
Also I leave my truck with my brother a lot, So he will need keys, That would leave me with 1 key it one gets lost....
It is always safe to have a spare key...
The chipped key is an anti theft device so some one who makes a copy of your key behind your back, they cant drive the truck....
Yes they can get inside, but if you don't have much of value inside, they would be looking to take the whole truck...
Todd Z