i've noticed some setups and speakers (ex: rainbow cmx 465's) that come with two woofers (not including 3 way setups)

i was just curious what are the advantages/disadvantages of this?
i figure tuning and canceling/phase issues *might* be a problem and also
i dont get how you could get even lose to a flat response without the use of two tweeters (i know dual tweeters arent ideal and will destroy your hearing IMO) unless you put half the power into each mid but than whats the point... may as well just double the power to a single woofer (if it can handle it)

am i missing something?