We always book at least a balcony category, because we like the natural light and ability to walk outside when we want. I am a bit claustrophobic so inside cabins are not my preference, although I do book them when I cruise solo for the cost reasons.
Which category you book really can depend on the itinerary. A cruise with lots of scenery while at sea makes a balcony more useful. Alaska and cruises to Canada or around Hawaii spring to mind. Cruises with many days at sea, such as a trans-Atlantic would make an inside cabin more logical.