For Privlages, have to think Rank Vs. Billet.
A Billet is .. well where you work, or a Job Title, the oft mentioned Ensign Kim has a billit of Chief of Operations ( Same as Data) on the Voyager. He works Alpha shift ( presumably 7am - 3pm ship time). A Privialge of this billiet is his own quarters. Now say there's another ensign on Beta shift (3p-11pm) they would not get there own quarters and have to shaire because they are not the department head.
Think of DS9 or submarine captains of old, they were only comanders, but they were the "Captain" of the ship or station. I think in some episode, we had a Lt. "Captain" of a runabout. Those people got the captains quarters.
Data's "Billet" is of 3rd in command. On the ship, you had Captain and Comander, then him. There were other people of higher rank than him on the ship, Troi, Crusher, Geordi, but there "Billet" was not on the command staff. Those 3 can take charge because they have undergone the training, even taking a command shift on say, Beta or Gamma shift, but there not in the ships chain of command. ( Data experienced the Ensign Kim disease of no rank promotion over the series.. I mean Troi got promoted to comander when she passed her command class, but Data doesnt??)
Now usually, a person doesn't remain an ensign for to long, maybe a year, 2 at most before there promoted, but in star trek, the billet may have a topped out rank structure. Like on Tapestry, Picard was only an Lt. because he was in the science division, or specialized division like biology. The team leader may get promoted to a higher rank, but the proletariat wont unless they become a team leader, or transfer to another track.
Now, a privlage on ship may be, better or more welll placed quaters ( away from the elevator please!) choice of shift, choice of leave time, more holodeck time,or better time choices. there are plenty of "Perks" of gaining rank or job assignment.