Why there is still 1.7k tris in an empty scene（Unity5.2.1）

HI guys, I am not sure if this is already answered somewhere, but i didn't find the answer by searching on the forum, check the following picture:

it's totally an empty scene, why stats show there is still 1.7K tris and 5.8K verts?

 

It's probably the skybox. Remove skybox from Lighting inspector and you will get 2 Tris, 4 Verts and 1 Batches. Remove camera and you will get 0 0 0. Congrats! Your game is optimized and ready for publishing

 

by the way can somebody explain me how Unity's tricount works? I mean I get additional verts from turning shadows - how could it be? My guess is that it counts verts in each rendering pass if I understand it right. More passes = more times the exact same geometry is rendered?

 

Correct, and there's often more passes than people realize.

Do you have real time shadows?
The main shadowing directional light is +1 or more passes. One for each cascade, plus one for forward rendering path calculating the scene depth because forward renderer does the first directional light's shadows as a deferred pass.
Shadowing spot lights or additional directional lights are 1 additional pass each just from the shadows.
Shadowing point lights can be 6(!) additional passes, again just from the shadows.

Do you use any image effects that use depth or depth and normals while using forward rendering? Depth based ones might require an additional pass to calculate the depth if you don't have directional light shadows. Normals requires an additional pass.
Some other image effects use other unique passes for things like a motion vector pass.

Do you use shaders that have multiple passes?
Many toon outline shader render geometry twice.
Multiple real time lights (regardless of if they're shadow casting) can render the model multiple times in addition to any shadow passes (controlled via the per pixel light count under quality settings).

Do you use reflection probes? Those might 2x the number of draw calls for some scenes, each.

 

Add Price tag and publish on all platforms, you are ready to be billionaire