For Secession Campaign I have a major power(the Alliance) taking on a band of rebels(the Pioneer Republic) where the numbers stack up heavily in favour of the Alliance. In theory the alliance can afford to take the long view and fight a slow steady war of attrition against the rebels. Dramatically that wouldn't have been very satisfying, something had to put the Alliance under pressure to win the war fast. The answer I came up with was economics, the territory controlled by the Republic created the wealth that propped up the economy of the rest of the Alliance. Take that wealth away and the Alliance is facing a crash on the scale of the Great Depression.
In a universe of interstellar travel and trade there are other economic issues that have fascinating implications. We're living in a world where currency is increasingly digital, but that depends on a global computer network able to handle transactions in a fraction of a second. If your universe lacks Star Wars instantaneous communications (or Star Trek replicators for that matter) what happens when you have to pay for something one planet and your bank is on another? Your going to need an honest to goodness hard currency, it may even be the case that your currency has to revert to the ancient system where coins had to made of something intrinsically precious, Silver, Gold, Unobtanium. Of course what if what constitutes precious differs from place to place? Perhaps your interstellar civilization runs on a barter economy.
All of this has potentially dramatic implications. In a fictional universe where currency is dependent on some precious material then a major find of said precious material could be the catalyst for competition and conflict. Where there is no currency any interplanetary power may behave in a thoroughly feudal manner, with taxes paid with foodstuffs, raw materials, manufactured goods, or even labour if a world has nothing else to offer. Tax collectors in that situation won’t be accountants sat in an office building, they’ll be the kind of people willing to make others part with their worldly goods to keep the state running.
Even if you have no interest or need to work economic matters into your story itself it can still play a valuable part in world building, helping to add texture and context to the back story. It can provide motivations for your characters and obstacles for them to overcome. In the immortal words of the Notorious B.I.G. "Mo’ Money Mo’ Problems" and problems help to drive plot.