The closing tag of a PHP block at the end of a file is optional,
and in some cases omitting it is helpful when using include()
or require(), so unwanted whitespace will
not occur at the end of files, and you will still be able to add
headers to the response later. It is also handy if you use output
buffering, and would not like to see added unwanted whitespace
at the end of the parts generated by the included files.