The other night, a friend and I were talking about plot holes and unresolved threads in Star Trek and something occurred to me about Jadzia Dax. The thing about Dax, you see, is that she is the only dedicated science officer we meet in the 24th century shows. Voyager doesn't have a science officer, unsurprising given she's not an exploration vessel, and on the Enterprise-D the job is effectively split between Geordi and Data.
The question that occurs is that Dax was assigned to DS9 before Starfleet knew about the wormhole and the strange new worlds on the other side of it. So why does a random Deep Space station in the middle of nowhere need a science officer when the flagship of the fleet doesn't?
So here's my utterly pointless headcanon reason: she's there to supervise the Starfleet relief efforts on Bajor. It isn't something that gets much play after the pilot episode but the main purpose of the Starfleet presence on DS9 is to do everything “short of violating the Prime Directive” to get Bajor up and running again after the Occupation.
Jadzia is there to help with the scientific side of that process like supervising agricultural projects or setting up genetic databases so families separated during the Occupation can reunite. Given that the chief engineering officer is a CPO (O'Brien) and never seems to work on anything not related to the station or its vehicles (runabouts, Defiant, so on) she's probably involved in the logistics side of things: what tech to send where, what Starfleet's industrial replicators should be churning out for the reconstruction effort and so on.