Top and Back wood?

[fenderbender4]

Thought I'd ask this question here as people seem to be familiar with tone woods. There are a lot of guitars that have a top and back wood combo, but was wondering what effect, if any, adding a back wood to a guitar? So say a Maple top on swamp ash vs. a maple top, swamp ash middle, maple back. Would it make it sound closer to maple? Or would it just kill the sound because you're basically increasing the number of pieces to the guitar body?

I've only seen this on a few custom guitars and then the really cheap imports, where they use laminates (at best).

Thanks in advance!