Been using doggie-doors for the past 20 years. I use two, one from the house to an attached shed, that can be closed, and then another from the shed to her graveled outside run, with a gate to control access to the entire fenced yard, so I can keep her in her run, if it’s muddy etc. In all that time I have only had one intruder, a feral cat, that didn’t stay long.
While not necessary, they are sure nice. During the winter months we stay in Florida with my sister and her cat, that is not allowed outside. So we spend a lot of time letting Jewel in and out. I know for sure she never needs to go outside anywhere near as often here as she does in Florida.
My dogs have never abused the door privilege, in and out, etc. Jewel spends her time where I do. She will go outside to investigate something, maybe bark a few times, then comes back inside. Pleased that she has sounded the alarm, and then goes back to resting, or whatever. But she never goes inside if I am out in the yard, and on the rare occasion that I leave her home alone, she usually waits outside for my return.