"building BVH"

Blender does something called “building BVH”.
there is an option “Cache BVH” and it says : “cache last built BVH for faster rerender if no geometry changed”
two questions:

  1. what does it mean “geometry changed”. if I have a moving character the geometry is changing? it’s the same mesh, just in a diffrent pose…
  2. will it get the render slower if I have just one single image?

Hi, this setting make not much sense anymore since building BVH is now multi threaded.
It was single threaded first and building BVH need more time than render sometimes.
It still help if have a huge scene and test materials or lightning.
Kepp in mind it write big files to your harddisk, sometimes GB´s and they are not deleted if you stop working.

Cheers, mib