It’s ok if they have zero use for you. In my case I have a camera that points out a window to the front porch. That cam has the pixel changing notifications on, which work great for packages being delivered (and also notifs from when the neighboors get home and use their headlights to light up the porch). I also have a camera inside the kitchen that faces the front door and the garage service door. I will be using my contact sensors on my interior doors to send notifs because I don’t want the pixel changes to tell me my cats are jumping around inside. 
Now if I get a notif that my cats are opening doors, then it’s on to plan b.