What's the diference with these 2 functions, StaticBatchingUtility.Combine() and Mesh Combining?

So my question is whats the diference with these 2 functions, StaticBatchingUtility.Combine() and Mesh Combining?

We want to load our levels with our system so instantiating it when on startup and and as we use light maps we cant use dynamic batching and therefore want it to batch so is StaticBatchingUtility.Combine the same as setting it to static or do you combine the mesh like the Mesh combining script from unity?

Also when having static objects that batches it adds an overhead to the file size in the level section, and when using the StaticBatchingUtility.Combine you make the file size smaller, this will increase the in game memory usage, but when batching it in the editor will it still be in the ingame memory ?

// Patrik