This is incredibly inefficient. I pay $40-$50 for a hardback book just so I can do all the work of cutting out a few pages and dropping them into my campaign? Including any necessary conversion to my local setting?
You said you liked having dungeons and adventures to drop into your homebrew campaign. Each hardback from Wotc is chock-full of dungeons and adventures you can drop into your campaign. How is that inefficient? Most of them are structured in such a way that they won't require a lot of tweaking to be used as standalone adventures (I know, I've done it a number of times now). As for converting to your setting, wouldn't you have to do that anyway, no matter where you're getting the dungeons and adventures you're dropping into it from?
I used the "Trouble in Red Larch" intro from
Princes of the Apocalypse as the intro to my homebrew campaign. I also used several other pieces from PotA as standalone adventures. For instance, I used the fire cult's surface and initial dungeons as an adventure tied to one of the PC's backstories. I also used the air cult's surface lair as a "random" adventure site that the PCs investigated. I also used the Amber Temple from
Curse of Strahd as a means for one of the PCs to obtain the power to bring his dead sister back to life. On top of that, I used the Fane of the Sun Swallower from
Ghosts of Dragonspear Castle, Neverlight Grove from
Out of the Abyss, and some old Dungeon adventures I converted. It made for a fun campaign. It really wasn't difficult to use any of those parts separate from the campaigns they came with.
And the books were all still useful in other ways too, even though I wasn't running the main stories out of any of them.
Out of the Abyss comes with handy rules on traveling through the Underdark, for instance.
Believe me, if it was truly inefficient, I wouldn't have bothered. But I found it quite easy. In fact, I believe quite strongly that WotC have deliberately written these big campaigns so that you can cut them up and use their parts in your own campaigns with little effort. That is most likely part of the reason why some people complain that their plots are so flimsy - it's because they've deliberately left things loose so that you can ignore the main plot and just use the parts you like.
This is like saying "the nice thing about buying a new car is that the tires can be taken off and put on another car". This is not a "nice thing". It is, at best, a way of salvaging some value from an AP you have no intention of running.
More than just the tires! The engine, the exhaust, the doors, the seats, the stereo, the wood panelling, etc etc etc.
