If you could let us know which ship you are referring to it would help in giving a more specific answer.
There are a number of ships that have "humps". The Radiance class of ships on Royal Caribbean and the Millennium class on Celebrity are two of the examples.
Often the "hump" cabins are a tad larger and may have a larger balcony. There are a couple of hump cabins on Radiance class ships that have "smaller" balconies and you need to look at the deck plans to see this.
These cabins are also centrally located and close to elevators and atriums.
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Like Mike said some balconies will be larger on hump cabins; but to answer your question; most people book hump cabins for their view; their balconies jut out a little further than the regular balconies; thus the hump of the ship. You can look forward and aft and the view is good; no obstructions.
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