Reusing assets / performance question

Hey, I have a quick question regarding performance and game design.

How important is it to reuse meshes from a single source asset instead of duplicating it multiple times in a larger asset?

For example say I built an arch in Maya, I could save it and reuse that file many times in Unity to create a castle corridor.

I could also duplicate the arch multiple times and build that corridor in Maya.

My question: is there a noticable benefit to working with assets assembled in Unity vs entire scenes built in a modeling program?

Thanks!