Is occlusion culling sufficient?

I have a question about optimal object placement/creation.

To use a simple example, if I have cubes, created with 6 different planes (one for each side), and I put hundreds of these cubes together, most of the sides will not ever be visible (and often complete cubes will be hidden). Using occlusion culling I can see that all of the "hidden" sides of the cubes are not shown, as expected.

My question is: is there any benefit to taking all of the time and effort to manually remove each plane that will never be seen, or is the occlusion culling sufficient?

Additionally is there a built in process that could highlight or remove such objects?