# combined chunks (of # source) in .im file: ###.im
The file in question contains a large number of render chunks which in turn will result in a large number of draw calls. This probably indicates that the mesh is very inefficient and will perform poorly.
The 'combined chunks' number indicates the number of unique draw calls which will result from the mesh when used standalone. The 'source chunks' number indicates the number of render chunks actually specified in the file, before any attempt is made to weld the chunks.