From a reading perspective, getting into a series is great. Once you’re familiar with the set up of characters and the backdrop their tales are told against, reading a new book in the series is like curling up in a comfortable chair, the fire lit and a glass of your favorite right to hand. Time for a good read. Yes, it’s that comfortable. You know in advance it’s going to be good. You already know the background, you don’t have to learn it. It’s easy to slip into the right mindset, the right place in the story and find out what your favorite characters are up to this time, or even meet new ones.
Writing a series is good, too, pretty much for the same reasons. When the galaxy has been sorted out (I write science fiction) and you know who’s who, writing is faster and easier because the backdrop is already done, already there, already wonderful. The politics are sorted, the structure, the scope.
Not only that, it grows. You solidify what you already have and it expands. New characters bring with them their stories and, with that, new facets of the whole are generated.
A quick glance at the galaxy I created shows that the Khekarians own just over half of it. They are distantly related to Terrans, aggressive and the instigators of a century long war with the Chiddran, who own a full third of the galaxy. That makes the Terrans the latecomers and the weakest, owning only a tiny sliver of what’s left. They are neutral in the scheme of things, but everyone knows that the Khekarians have their eye on mastering the entire galaxy, so things can get a little tense.
This gives me a lot of planets, people and societies to play with, all with the same backdrop (the Khekarian/Chiddran war). The wonderful thing is, it just keeps branching out – the field is open, the scope unlimited. What’s not to like?