Include sources from subdirectories: target_sources or object library?

I have a fundamental decision to take on how to structure the CMake project layout of our (existing) project (1000+ source files). While there are some libraries, which I will include via add_subdirectory and add_library the majority of our components are organized in many subdirectories and included as source files.

Reading through @craig.scott’s very helpful Professional CMake, I tend to use add_subdirectory and target_sources. But there is also the option of object libraries: add_library(targetName OBJECT ...

When would that be more appropriate?

Personally, I treat object libraries as a last resort option. In most cases, static libraries are simpler and are better understood by developers. For specific situations where you have a clear use case that requires object files rather than static libraries, they may make sense, but it is not lost on me that it is an area that has been disproportionally represented in user questions compared to other parts of CMake.