As far as it goes for me. I ask each asset if it would need a normals. If it's essential, if it requires one, or am I just doing the pipeline at this point?
Most hero assets are going to merit one as the player is probably going to be up close to it, but lets say for a bottle, not as crucial as maybe rock that's used over and over again.
I leave it to my experience and me asking the asset what it needs. Sometimes things look better without normals, maybe a grayscale specular map is more effect in showing off what needs to be shown off.
All in all, I come back to asking "why does it need it?"
Everyone here is right though. In addition, the engine being used may have some preferences on normal maps and supporting maps, point being that unless it chugs, it's nothing to big to worry about, but it may come to that point where you need to cut back and work on runtime, normal map necessity is an area go at if the time comes.