I have run games in a few different styles, sometimes with a list of enemies and monsters and story on the fly; other times with a few sessions well planned

Right now I'm running a pretty cheap story, with procedurally generated landscape and dungeons, and stories inspired by the https://d20srd.org random adventure generator

Once years ago I wrote a plan for my group that ran to forty pages, but I knew them well and felt I could predict how they'd go - they were led around by the temptation of riches