One of the so-called rules of photography is to look behind you, and all around, on a regular basis. So for instance. This is a sunrise photo from a few days ago, and I'm looking west. The sunrise was sort of interesting, but nothing special. Then I looked over my shoulder.
It's a good idea to stay alert while shooting. Yes, to some extent you need to be focused on the subject, and thinking about what settings on your camera might make things even better. But you need to be aware of what's going on around you while shooting. People move around. Just because they weren't there a minute ago, doesn't mean it's safe to step backwards or sideways.
Then there's what you're standing on. Often it's pavement or nice dirt. No worries. Except for curbs, gullies, and other surprises. One of my shoots recently was of guys working on icing a community skating rink. I wore traction aids for that one, and just about went for a ride a few times. The surface isn't quite flat and level yet.
Wading through the Fish Creek in the summer, or walking/snowshoeing on the ice is a wonderful experience. Until you slip and get you, your camera, your phone, and your wallet wet. No fun there, and fortunately that is not the voice of experience. My rule is to either take photos, or move, but not do both at the same time.
Then there's the reason not to look behind. Someone or something might be gaining on you. Sometimes it 's better not to know. I'm remembering that Far Side cartoon 'Objects in the mirror are closer than they appear.' All the driver can see is an angry eyeball.