Question about draw calls

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I'd say with something relatively small, like said banister, it would be better to have it be one mesh. A whole fence surrounding a huge meadow on the other hand should probably be broken up into a few smaller repeating fence parts.
I guess it's best if you just look at the original Amnesia meshes for reference and see what they put in one mesh and what they decided to build from smaller ones. That should give you an idea on how big the meshes should be

Also keep in mind: For drawcall reducing, meshes need to use the same material, not just the same texture.