Hello Giannis,
No, I consider this an unnecessary and bad advice. It makes no sense and I will tell you why.
Joomla! can read the information on the file. If it couldn't it wouldn't work. If a hacker finds a vulnerability which allows him to dump Joomla! configuration variables he can dump them just fine.
If a hacker manages to install a C99 or similar script on your site (which allows him to view and edit files) it's quite trivial to open the configuration.php file, read it, see the real location of the configuration data and read the data just fine. If he's using an automated hacking script it's equally easy including the file and getting a dump of all configuration variables.
Therefore this advice is snakeoil security: it claims to improve your security but does nothing. It's like wearing a cardboard "bulletproof" vest. It won't stop any bullet but it will give you a false sense of security, ending up in killing you rather than protecting you.
Moreover, moving the configuration.php outside your site's root will cause a site restoration with Akeeba Backup lose all your configuration settings or even cause a restoration failure. Akeeba Backup expects to read the configuration.php file. Since it doesn't contain configuration files but tries to require() a file in an upper level, if the file doesn't exist the restoration will crash.
My advice: don't move the configuration.php file. Any non-lobotomised hacker can overcome that rudimentary measure in 10 seconds at worse.
Nicholas K. Dionysopoulos
Lead Developer and Director
🇬🇷Greek: native 🇬🇧English: excellent 🇫🇷French: basic • 🕐 My time zone is Europe / Athens
Please keep in mind my timezone and cultural differences when reading my replies. Thank you!