Among my reasons for deciding to use the adventure path was time. I have a job which consumes a fair amount of my creative energy. I have a family, including 2 young boys, I want to spend time with. And I have a bunch of other creative projects I want to work on in my free time and I wasn’t sure how much time or energy I would have to design and run my own campaign. Couple that with the reality that I was starting with completely new players who’s only gaming experience was with D&D which is notoriously time-intensive for the GM in terms of prep and my decision seems obvious.
I should know better than to think I am ever going to not work on a campaign between sessions. I have still spent hours each week prepping for the next session, planning long term story elements and so on. The difference is that I have done so voluntarily and almost none of that time has gone into writing down stats for monsters, painstakingly designing EL-appropriate encounters, or figuring out what to put in treasure hordes. I have been able to put my focus entirely on story, NPC’s, and plot development. I know the stats for the monster they’re going to fight this week are already in the book. I can worry about the dialogue I want them to have before they’re dragged into the fight. The adventure path has done most of the boring work for me.
Furthermore, I really CAN just run a session from the book without much additional prep at all. I don’t usually choose to do that, but if a week gets really busy it won’t mean having to cancel our game because the GM isn’t prepared. I can crack open the module 20minutes before game time and be ready to go.