The features provided by coqoune is currently rather primitive, compared to more mature Coq environments like coqIDE, vsCoq, etc. The benefits of coqoune is basically those of the kakoune editor, for example:
kakoune features a great modal editing interface as improvement of that of VIM, as well as multi selection support, offering a unique editing experience.
kakoune itself is very lightweight, and relies on interaction with external tools to do various staffs. For example, in coqoune, you can display your goal and result in another terminal emulator using window managers like i3, or using terminal multiplexers like tmux. This is a feature not found in all current Coq environments, as far as I am concerned.
Although coqoune is quite simple, it is fast and usable. So if you like kakoune and Coq, you’re free to pick them both now. And I sincerely hope we can see more choices in the Coq eco-system in the future.