When on, Vim will change the current working directory whenever you open a file, switch buffers, delete a buffer or open/close a window. It will change to the directory containing the file which was opened or selected. When a buffer has no name it also has no directory, thus the current directory won't change when navigating to it. Note: When this option is on some plugins may not work.

(default off)

only available when compiled with it, use exists("+autochdir") to check