Noob question: foo/mod.rs vs. foo.rs + foo/ for module directory

Rust beginner here, and I am a little confused by the motivation of declaring module by using <mod\_name>.rs and <mod\_name>/ (in edition 2018?)

Why was it necessary to introduce this new way of declare a directory based module? Seems it doesn't achieve anything substantial over <mod\_name>/mod.rs approach? Features usually are added to compilers with much consideration and scrutiny, and this seems to be a purely subjective/preference thing.

Of course I am missing something here, and would like to find out.

Thank you!

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