That box is for the motion sensor lights that Kevin installed, and we want to continue having on for night time when the bottom lights are turned off.What is happening with the non-symmetric octagon box on the garage? Sconce boxes look fine but the higher one should probably have a match on the left (and the wire you have coming out for probably a camera is one board lower).
As for degradation, It should be the white trim board that takes a beating. Easy enough to replace a short section of that if it starts to look beat up. I would shim it during install so it doesn't actually touch the concrete (trim a saw kerf off the bottom if needed to make the space).
Yes, it would only be the white trim that takes a beating. I'm almost tempted to install flashing that runs down the width of it to protect it from the elements. May look a bit off....but it'll be protected. Better than that abomination.