When adding details, how do I know if I should model them as a part of the mesh, or use a normal map (or other textures)?
I know this is an opinion-based question, so let me try to narrow it down. For example:
Can we make these grooves with normal map only? And if so, what’s the pros and cons for texturing instead of modeling them?
A more complex example:
If someone asks you to make a 3D render like above, how do you know which details should be made as geometry, and which to be on textures?
Hey man! I would say it depends from case to case, but for me, I use normal maps whenever I would require too much geometry to recreate the same detail in 3D or whenever the detail is too fine.
Pros of texturing: less geometry, depending on the texture used you can have many “natural variations” directly
Cons: it might not look as detailed, depending on the texture, it kight look tiled if you use a small texture etc
In the complex case I would model everything and use a normal map only for the leather texture
Also, I do Blender as a hobby so I might be very very wrong but this is my opinion 
The question here is: for what purpose?
I probably didn’t narrow it down enough… let me try to rephrase it.
Can this jagged silhouette be made with normal/bump/displacement map?
If not, it’s a limitation of normal/bump/displacement map. What are other limitations of normal/bump/displacement map? If it can, how?
With a displacement map made by modeling it and baking to d-map… or even paining it… then the model have to be subdived or in newer game engines ther is a displacement shader… nevertheless it depends on the accuracy you need to accomplish.
