Each book needs a good beginning and a good ending. People get pissed off when you don't close things off properly at the end.
Patrick RothfussStand alone books are nice because they have everything all in one tidy little package. Neverwhere was awesome because you get action, adventure, character development, the exploration of a strange world, PLUS resolution of all the problems and mysteries at the end. No lines no waiting. That's very satisfying. Multi-volume stories are satisfying too, just in a different way.
Patrick RothfussBut it isnโt a rough draft either. The one I turned in several months ago was rough. There were some bad plot holes, some logical inconsistencies, pacing problems, and not nearly enough lesbian unicorns.
Patrick Rothfuss