Every polygon in a mesh entails a rendering performance hit insofar as a GPU needs time to process and render each polygon. Consequently, it's sensible to minimize the number of a polygons in a mesh, even though modern graphics hardware is adept at working with many polygons. It's a good practice to minimize polygons wherever possible and to the degree that it doesn't detract from your central artistic vision and style:
High-poly meshes! (try reducing polygons where possible)
There are many techniques available to reduce polygon counts. Most 3D applications (such as 3Ds Max, Maya, and Blender) offer automated tools that decimate polygons in a mesh while retaining their basic shape and outline. However, these methods frequently make a mess of topology, leaving you with faces and edge loops leading in all directions. Even so, this can still be useful for reducing polygons in static meshes (meshes that never animate), such as statues, houses, or chairs. However, it's typically bad for animated meshes where topology is especially important:
Reducing mesh polygons with automated methods can produce messy topology
If you want to know the total vertex and face count of a mesh, you can use your 3D software statistics. Blender, Maya, 3Ds Max, and most 3D software lets you see vertex and face counts of selected meshes directly from the viewport. However, this information should only be considered a rough guide! This is because after importing a mesh into Unity, the vertex count frequently turns out higher than expected! There are many reasons for this, which is explained in more depth online at:
http://docs.unity3d.com/Manual/OptimizingGraphicsPerformance.html.
In short, use the Unity vertex count as the final word on the actual vertex count of your mesh. To view the vertex count for an imported mesh in Unity, click on the right-arrow on the mesh thumbnail in the Project panel; this shows the internal mesh asset. Select this asset, and then view the vertex count from the preview pane in the Inspector object.
Viewing the vertex and face count for meshes in Unity
