I played a lot of D&D in my day (Mentzer Red Box in junior high, AD&D 2e in high school, and D&D 3e for many later years), and I did lots of adventure prep - maps, monsters, treasure, all that jazz. It was often fun, but the older I got, the less time I had to do it.
Finding new-fangled low-prep/no-prep games a few years back was great; my gaming, in general, is more fun and less stressful. Even for games that require some prep, I'm pretty comfortable winging it.
This past weekend, a bunch of old friends got together for an epic D&D game (we played Dungeon World), and - for whatever reason - I reverted to my old habits. (I even got a little panicked about not having enough cool stuff and started a thread
to solicit ideas.) I ended up with ten pages
of adventure notes and monster stats, two different sets of mini-handouts for moves and questions, and a map that I re-drew because the first one didn't look cool enough. I totally nerded out.
And the game was really awesome.
All that prep made for a different experience. I didn't invent much of anything on the fly. I knew what the inn was like, who the townfolk were, what the wounded fae warrior in the forest had to tell, the bridges, the traps, the dungeon layout, the field of undead - the whole nine yards. I even wrote flavor text.
Having all that info let me bring more inventiveness to the actual encounters in terms of description.
Which is not to say that I plan to go back to this style of GMing. For one thing, there's no way I could spare the time to regularly prep for games like that. Plus I really like the make-it-up-as-you-go school of gaming. But I'm glad I put all that work into my epic D&D reunion game.