Why my Rust doc directory is common for all my Rust projects

I got criticized in one of my post why I put a documentation for the app inside its doc directory instead of putting Rust documentation there. So, I would like to get a wider opinion if I do something wrong. Rust doc has a very neat feature allowing to merge documentation for projects or/and crates in one integrated HTML doc system. In this case, I do not need to switch from one documentation for some crate to another documentation for another crate, because all my crates already transparently ...