As the notice being said, the Imagick module is optional and not really necessary for most websites.
The PHP Imagick module is disabled mostly due to the fact that it has many bugs and has a big vulnerability, the CVE-2016-3714, also called Image Tragick.
And that’s not really the reason. The main reason it will not work and it is disabled because:
It uses shell-access functions such as exec() & system() and shell functions are not currently supported on free hosting.
I hope this info may help 