When you need to including file, please recheck file content that will be use. If file is not contains PHP codes, use readfile() function to increase performance.
Because files that including with readfile() does not parsing by PHP. It will be different with construction language include() and require(), and files will be evaluated before.

Consequence from using readfile() is increase attack risk. This risk will be happen when accessing file from URL.

Solution for the attack risk is by using File Handling.