You moved the light stand - now your lighting has changed.
And it's not situations out of the norm... Or are you going to go out of your way to rearrange every little item on a table a bridge and groom are sitting at, or ask them if they could just hide their cellphone somewhere quickly, or go move the stand a speaker is on, or ask someone to go change their jacket to get rid of the stain they got on it, or do a variety of other things not unlike this at a wedding?
How about telling that kid that suddenly popped into the second photo of a burst of shots of someone playing a volleyball match on a beach, or a photo you were taking of a surfer? Are you going to completely discard the second out of three photos because the kid got in the way, or edit it?
Taking photos of a family in a park - some small dog suddenly runs through the frame, but the photo was otherwise exactly what you were looking for. The dog's presence doesn't lend anything to the photo at all, it's purely distracting - the family didn't acknowledge its presence in the photo that mattered.
There are MANY situations that wouldn't be 'out of the norm' where you simply cannot feasibly go about 'taking a better picture', because the moment has already passed or to try and fix things would waste time or cause you to completely miss a moment.