By activating the environment above you are able to leverage the binary cache Spack introduce recently. If the cache is already filled with the architecture and operating system you desire.
Installing a package without dependencies will show.
spack graph pkgconf spack install --no-check-signature pkgconf
In case you are using a combination of distribution and CPU microarchitecture already present in the binary cache, the pacakge and all dependencies will be fetched from binary cache instead of building everything from source.
patchelf is always build from source. :)