Chrome's headless mode is made for headless/server environments, such as where you may automatically want to be capturing screenshots of rendered pages, etc. This is very practical for automated testing. Or there's the use-case of just wanting to interact with the DOM but not caring about presenting the contents on any connected physical display.
Chrome picks up a --headless switch for launching the browser in this mode. Remote debugging is also still possible in the headless mode. This mode for Chrome will be supported on Windows, Mac, and Linux. Firefox has similarly been working on this functionality but it has yet to land.
More details on the headless mode here. Other changes expected for Chrome 59 include Android support for the W3C Payments API, CSS line-height-step support, a feature policy to allow sites to enable/disable browser features and APIs, piping for the Streams API, and other changes. The Chrome 59 branching is expected this week while the stable debut should happen around 6 June.