Why would one omit the close tag?

Question

I keep reading it is poor practice to use the PHP close tag ?> at the end of the file. The header problem seems irrelevant in the following context (and this

Answer 1

Well, I know the reason, but I can't show it:

For files that contain only PHP code, the closing tag (?>) is never permitted. It is not required by PHP, and omitting it prevents the accidental injection of trailing white space into the response.

Source: http://framework.zend.com/manual/en/coding-standard.php-file-formatting.html