From How does the Death Star gravity work? we learn that:
Gravity within the battle station was handled by omni-directional gravity boosters built into the decks, walls and ceilings. These gravity boosters changed orientation as easily as flipping a switch, and they were designed to allow the gravity orientation to be altered from sector to sector, or even from corridor to corridor. While hangar bays imposed gravity perpendicular to the Death Star's core, adjoining corridors shifted the gravity orientation to coreward. [...]
Source: West End Games D6 Roleplaying Game (Second Edition) supplement Death Star Technical Companion, Chapter Two: Technical Specifications, p. 16, right column (source uncovered by BMWurm)
So while those omni-directional gravity boosters allow to adjust orientation on a per-sector basis and also to make transitions in between (e.g in the turbolifts), why make the orientation different in different sections?
I'll go with the explaination of the Emperor's Throne room (see Why was the Death Star's tractor beam not used as a weapon during the battles?) and dismiss windows in the walls as an aesthetic choice of the Empereror. But what about other sections?
A prominent example are the hangar bays. While most sectors show a coreward gravity orientation, i.e. the deck you walk on is a sphere (just like you'd expect on any celestial body) and the walls are perpendicular to it, the hangars are different. There gravity is perpendicular to the rest of the station. The hangar deck is that what would be a sidewall in other sections. A fact not only stated by the source listed above but also well established in the movies ANH and ROTJ. However hangars would just work fine if ships where to land coming in from the "roof", e.g. land like on a real planet.
So, what is the rationale for this design choice?