For the functions like is_file(), file_exists(), etc PHP caches the result of this function for each file for faster performance if function called again. But in some cases you want to clear this cached information, for the task like getting the information of the same file multiple times in same page.

Other methods this cache effects include stat, file_exists, is_file and more. If the state of a file is changed during the course of the script - say it's deleted manually, not by PHP, your script may not recognize that. By calling clearstatecache, you refresh this cache and make it possible to see the latest file system info.