Inverted beams are the same as upstanding beams. As already mentioned in some answers, it is used for headroom clearance. Bottom line is, wherever there is a restriction on maintaining a certain level of beams due to reasons like aesthetics/maintenance purpose, we increase the level of beams. Technically speaking it is not the same as putting higher reinforcement on top of having a flexural tension at the top and so I personally don't prefer to call it an inverted beam, and rather calling it an upstanding beam should be better.