The edition system was created for the release of Rust 2018. The theme of Rust 2018 is productivity. Rust 2018 improves upon Rust 2015 through new features, simpler syntax in some cases, a smarter borrow-checker, and a host of other things. These are all in service of the productivity goal. Rust 2015 was a foundation; Rust 2018 smooths off rough edges, makes writing code simpler and easier, and removes some inconsistencies.