PCHs give a sour taste in my mouth after working on a project which very liberally added commonly imported headers to a huge one. In practice, it meant each TU was indirectly including many more headers than needed, and it was harder for humans (or IDEs) to reason about the real dependency chain. While builds were faster, they also started using much more memory.

You also can end up needing to rebuild the world, if touching a header that is part of the PCH, even if it isn’t really needed by all the targets.

Modules and header units were supposed to solve these a lot more cleanly, but is still not well supported.