One of the reasons why I believe that campaign homebrewing is best is the fact that a dungeon master doesn't have to commit to an 'official' campaign. And Advanced Dungeons & Dragons first edition had this in spades. One could take Greyhawk & mold it into their own home campaign setting.
And this also relates as well to Dave Hargrave's Arduin campaign setting. Arduin is small, very detailed, and highly dangerous. And I often feel that Arduin campaign setting books are the ultimate old school rpg tool kit.
Homebrewing Arduin has the potential to plunge the PC's into the deep end of a Hargravian campaign. The Nexus gates of Arduin make it likely that PC's could potentially run into just about anything within a dungeon or campaign encounter.
And this was something that came through in DM Steve's Arduin campaign where we came face to face with the Great Wurm road's enterance in one of his dungeons under the city of Kells. The enterance was quite literally the enterance to the underworld of Arduin. Each time we came near the monsters got far more deadly. The Great Wurm road comes from Shadowlands (Arduin Grimoire volume 7) from 'The Underworld of Arduin'
The encounter with the 'great Wurm road' cemented our insane greed for some of the rumored treasures. Treasures from these areas were fetching top coin from the wizard's guilds. And among our number were a set of wizard thieves.
The Great Wurm road made the Underdark of Forgotten Realms look like 'Anne Mazi's Farm Ride & Petting Zoo'. We had came face to face with many humanoid races & even worse things within the interior of DM's Steve's campaign. And we did get our treasures but the cost was pretty damn high.