less materials is better in general but it doesn't make any difference whether the mesh has multiple materials on it or not cos it'll get broken up by material when rendered anyway separate parts is a generally a good idea for stuff like windowframes or anything relatively dense since you can re-use it an thus save memory…
Here are some potential problems with not combining a mesh: * Some engines have problems with lighting when you have open edges on a mesh. You get light leaking. * Some engines will be creating LODs automatically for your buildings. Having open edges can confuse the LOD algorithm and create a bad LOD. * If your engine uses…