How expensive is the same asset in the game?

Let s say I use the same meshes again and again in my game. Is this cheaper than using different meshes?
Has the computer to calculate only one mesh for different places? Or are the meshes distributed over the level with fixed positions, so the computer has to calculate all of them???

Thanks in advance

If you just place static meshes in your scene then yes, your machine still has to calculate all the visible polygons. However if they share the same texture it is not that big of a deal, since the draw calls are reduced.

I think it is a different story if you are using the foliage tool for painting trees on a terrain. Some meshes will then be combined in a cluster to further improver performance.