Does scaling meshes in the editor affects the game’s performance?
For example:
64x64x64Units cube scaled by 8x16x4 to get a 512x1024x256 sized cube.
also how does it affect the lightmap of the scaled mesh?
Theoretically the answer is no. The object has the same amount of polygons and probably similar textures. The resized cube may also be use to occlude/cull whatever is behind it, which actually improves performance. However, you are scaling up and distorting your UVs and ‘zooming into’ your materials, which may or may not be what you want. The lightmap is also scaled up, so it may require a higher resolution to work at that size; last resort solution as you really don’t want 1024 lightmaps! I advice you visualize (upper left corner of your viewport) your maps and shaders to check for anything out of order.
Hope this helps 