> it finds modules in a bottom-up hierarchical fashion. That allows a single app or module to use modules that in turn use different versions of other modules, and not to worry about what other modules are doing
To my understanding, if your app transitively depends on package foo-1.2 in thirty different places [0], there will be thirty copies of foo-1.2 on disk under node_modules/ . Each package reads its very own copy of foo-1.2 when it require()s foo.
On a large app, that adds up to a lot of inodes ("why does it say my filesystem is full? there's only 10G of stuff on my 80G partition!" because it's used up all its inodes, not its bytes.) and a _lot_ of unnecessary I/O. The second through thirtieth copies of foo-1.2 don't come from the kernel's block cache "for free", they come from spinning rust (or if you're lucky, the dwindling number of IOps your SSD can choke out. Do you pay money for provisioned IOps?).
[0] and thirty is a lowball number for some projects, especially given the community's preference to require "leftpad" or whatever instead of writing a couple lines in their own projects
