I got all excited about changing a few of my cameras to 4:3 as it would be nice for a few cameras... only to find out that all the resolution options for those specific cameras are only 16:9. Got all excited for nothing.
That's how all cameras I've seen do it. The "main" or higest-resolution format is what is advertised, or standard. Other possible aspect ratios are crops from the actual sensor dimensions. That's the only way it can be done.
Most of the photo cameras I have are based on 3:2 aspect ratio because that is what 35mm camera film was (24×36mm useable area). But I have had a few cameras with different sensor aspect ratios. And all of the photo cameras I've had used square pixels on a square grid arranged to achieve the active area. But even that is not always the case. There are sensors that have non-square pixel grid arrangements.
My dad had SpeedGraphic film cameras that used 4 x 5" and 2.25 x 3.25" cut film. Those were standard "press cameras" and he had used them for sports photography back when he was in college in the '40s.
I grew up shooting 120 roll film, then 2.25 x 2.25 format on roll film in a twin lens reflex Rolleiflex of my dad's. A beautiful camera. Then I used a 35mm roll film viewfinder camera and eventually bought a 35mm SLR (Canon FTb) with lawn-mowing money when I was 14. From there, I used pretty much all 35mm SLRs, and that (2×3) aspect ratio is probably what's been burned into my brain as "normal".
But all aspect ratios have their uses.
While you are throwing away data when you choose an aspect ratio that is a crop out of a camera's native resolution, you are saving data storage space and lowering traffic load on your network and PC, etc. So there may well be benefits to choosing an aspect ratio other than the sensor's native one when setting up your security cams, especially if the extra coverage is completely useless.
On the other hand, if that extra coverage gives a second copy of a useful area, you might want to use it.
No matter what the camera's aspect ratio, it will never fit every situation. In photography, we often, perhaps most of the time, end up cropping the captured images to get the exact image we want. Standard prints or slides don't give you that flexibility. But when you make your own prints, or post to the net, etc., you can crop exactly the way you want. And cropping is a huge part of image composition.
Shoot wide, and crop for composition.
Then again, there is an art to getting great composition using the native camera "window", too. It's all fun.
For security camera use, just make sure you have plenty of pixels over the critical areas. This may not be fine art, but there is an element of art to getting things right, for sure.
