NOTE: This mod is included in The Fixes so you don't need it if you are already using that.
This mod improves bandwidth usage by reducing the frequency of specific data synchronization without compromising gameplay or visuals. It affects the functions responsible for sending your current position and look direction. The latter one is especially problematic since it has no rate limit it in vanilla which means you are potentially sending your look direction every single frame which is totally unnecessary.
This mod can help reduce desync drastically, especially on slower connections as you will be sending a lot less data to other players which reduces the load on your own as well as their connection.