Choosing your alignment appears to be as simple as, well, choosing your alignment; dark side characters won’t have to do extra work to “represent” the dark side. Subsequently, actions you undertake will influence an ongoing struggle while also awarding you with tokens to be used at cosmetic vendors. Once one side reaches victory, the war ends for a time, with both the victor and the loser getting a bonus to regroup and gear up for another struggle. It’s an ongoing system to influence the galaxy as a whole for cosmetic rewards; what more could you want? (Our own columnist has some thoughts on exactly that.)
Source: Official Site