I use C++17 in my toy code (which is for a mixture of fun and learning modern C++, so...) and the main reasons (besides to learn) I use C++17 over C++11 is std::variant and (from C++14) make_unique. C++11 has a lot of compelling stuff but 14 and 17 seem to be relatively minor improvements over 11. It’s a pity they introduce bloat... definitely makes them much less compelling for use cases where it matters.

Nested namespace definitions and structured binding declarations are also nice.