Saga, Series and Just Plain Long Books

Over at Tor, Katherine Kerr writes about 'the saga habit': book series' that stretch beyond what many readers consider a reasonable length, and explores why that happens:
Another risk: the writer can put a lot of energy into a character or tale only to see that it doesn’t belong and must be scrapped. When I was trying to turn the original ghastly novella into Daggerspell, the first Deverry novel, the most important dweomerman was an apothecary named Liddyn, a nice fellow...not real interesting, though. My subconscious created a friend of his, a very minor character, who appeared in one small scene, digging herbs by the side of the road. When the friend insisted on turning up in a later scene, I named him Nevyn. If I’d stuck to my original plan, that would have been it for Nevyn. As soon as I asked myself, “but who is this guy?” I realized what he was bringing with him: the entire theme of past lives. Until that moment, reincarnation had nothing to do with this saga. 
Liddyn shrank to one mention in one of the later books. Nevyn took over. The past lives appeared when I asked myself how this new strange character got to be a four hundred year old master of magic. What was his motivation? How and why did he study dweomer? These questions brings us right back to the idea of consequences. As a young man Nevyn made a bad mistake out of simple arrogance. The consequences were dire for the woman who loved him and her clan, and over the years these consequences spiraled out of control until they led ultimately to a civil war. The saga had gotten longer but deeper, and I hope richer. Had I ignored these consequences, I would have been left with an interesting episode, isolated, a little thin, perhaps at best backstory.
Full Story: HERE