Subwoofer meshes well with 2-channel?

I hadn't really given it much thought before, but will a sub work well with a 2-channel system (when reproducing music) or does it just muddy things up? I have full-range speakers (Tyler Linbrook Sig's) that go down to 30hz or so, and have 2 7" Seas drivers. I had considered getting bigger speakers that have more drivers, but this would be a more economical option, rather than getting some huge 300lb speaker that requires a crate to ship on.

If this the case, is there a particular reason that huge speakers are common, vs. a smaller speaker and subwoofer combo?