Shrinkwrap doesn't slim down the trees, it just makes sure the whole tree is locked to specific version, so your Linux server doesn't end up installing a different version of some package than your Mac does.
You might be thinking of npm 3, where modules are installed at the top of the tree first, and there's only extra copies of a module down the three if something specifically needs a different version of that module.
You might be thinking of npm 3, where modules are installed at the top of the tree first, and there's only extra copies of a module down the three if something specifically needs a different version of that module.