David Heinemeier Hansson wrote that the base install does not need them. Clang is a C compiler, and LLVM is the toolkit that travels with it. The Qt applications use a C++ compiler setting, Ruby arrives prebuilt, and the usual native gems build with gcc, another C compiler. The use he named is a Rust crate that generates C bindings. That needs the libclang library from the clang package, and Rust is not part of the base install.

The merged Rust setup command installs clang before it installs Rust. Removing that Rust setup does not remove clang. Hansson wrote that hiding every LLVM file still allowed Ruby to compile and a Rust extension to build, so the base list leaves out llvm as well as clang. He wrote that the ISO is about 87 MiB smaller and a new install about 460 MiB smaller. He opened and merged the change.