What is the use of mb_http_output (), given that output coding is usually fixed in other ways?

Throughout the Internet, including stackoverflow, it is suggested to use mb_http_input ('utf-8') so that PHP works in UTF-8 encoding. For example, see Problems with PHP / MySQL Encoding. instead of certain characters . On the other hand, the PHP manual says that we cannot fix the input encoding in the PHP script and that mb_http_input is just a way to request what it is and not a way to install it. See http://www.php.net/manual/en/mbstring.http.php and http://php.net/manual/en/function.mb-httpetinput.php. Well, this is just a clarification of the context before the question. It seems to me that in Apache + PHP + HTML there are many redundant commands for controlling the conversion from the input encoding to the internal encoding and, finally, to the output encoding. I do not understand the usefulness of this. For example, if the source encoding of the input from some external HTTP client is EUC-JP, and I set the internal encoding to UTF-8, then PHP would have to do the conversion. I'm right? If I am right, why should I enter the input encoding in php.ini (and not just pass the original one), given that it will be immediately converted to the internal utf-8 encoding? A similar question remains for exit. In all my htpp files, I use a meta tag with charset = utf-8. Thus, the final HTTP encoding is fixed. Moreover, in PHP.ini I can set default_charset,which will be displayed in the HTTP header in utf-8. Why don't I use mb_http_output ('uft-8') when the final output encoding is already fixed. To summarize, can someone give me a practical concrete example where mb_http_output ("uft-8") is clearly necessary and cannot be replaced with more ordinary commands that are often inserted by default in editors such as Dreamweaver?