That's great for a greenfield project where you're the only developer. If it's multiple people, you have to deal with whatever subset the powers-that-be on your team wish to use. If it's not greenfield, you have to deal with the subset exists in the codebase.

And if you're a Dirty Harry type like me, debugging issues with dozens of disparate codebases written in various crap subsets, you pretty much have to know the whole cursed thing.