This is a normal practice for applications, and allows you to pre-compile that header for performance. I don't think it's a bad enough practice to warrant complaining, but it's good for people to know the advantages or disadvantages.

See this: https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines...

Technically, headers are just copy-paste, obviously. However, there's value to keeping them as standalone as possible.

Headers should still be self contained, although precompiled headers are used. Those things are mostly orthogonal