It's less common with how players use cameras as well but the other thing that an embedded time code would enable is timeline sequences for photos.
If, for example, your character took three photographs in sequence of a shroud sprinting across the road and dragging someone into the sewers, then in-world someone could look at those photos and understand from relative changes in the scene that they were in a particular order and took place all in a certain short period of time.
From the perspective of us the players though it could just look like a photo of a street with one person on it, a photo of a street with two people on it, and a photo of a street with no people on it, each of which could have been taken months or years apart.
I raise that examine because it's actually something that happened to me the first year I started playing and it was a lesson how little context is preserved no matter how active the surveillance on someone is.