Performance Considerations

Easy Combine isn't meant to be a replacement of other optimization techniques currently present in Unity, but as an essential extension for good framerates. Generally, one always has to make a trade-off between all optimization techniques to benefit the most.
When combining your entire game world into one mega mesh, one could probably save draw calls, but the occlusion culling procedure cannot cull anything because the mega mesh is always in sight, which, in turn, results in more drawn geometry.

The best practice is to combine objects that can be put together in local visibility groups. Such a visibility group could be a table with all its dishes or a shelf with a bunch of books. This way, the occlusion system can calculate reasonable occlusion trees, and the system can cull a lot of the objects while the objects in sight have just a few draw calls.

One has to find the right balance between draw calls and occlusion culling group sizes to get the best possible performance.