most people use it to show the backside of the sub for install purposes, or for spacing issuses (not sacrificing the sub's displacement for cubic ft. loss inside of the speaker box)
these are the only 2 reasons that i can think of right now
i inverted mind cuz i didnt feel like getting grills and my subs and when i bought my subs i wanst sure if i was gona wire em up to 4 ohm load or 1 ohm load so it was much easier to re-wire the subs with them inverted. Also my subs cones i think are ugly compared to the magnet and baskets are so beefy and sick lookin.