And what is the binary danger of other functions?
For example: http://php.net/manual/ru/function.fwrite.phpFWRITE – Binary-secure entry to file

Answer 1, Authority 100%

This means that the function is suitable for processing not only simple text, but also binary data. Nothing is lost or distorted.

Sometimes it is necessary to work with binary data. For example, something to generate volumetric, and the result must be squeezed in the GZIP function GZENCODE . This feature will return the binary data string. Or data encryption functions often give exactly the binary representation – simply because it takes less memory, and in something text, if necessary, you can convert you already.

Functions not marked as binary secure, can distort the value or incorrectly process (for example, in the NUL symbol area), because Designed to work with the text. And binary-safe – will work correctly, which bytes were told to write down – those will be recorded.