The simplest way to install FreePBX is through the FreePBX distribution. It offers the advantage of installing a complete working platform with Asterisk and FreePBX in one go without having to worry about the correctness of the steps carried out in the manual installation process or in debugging errors. If you have little knowledge of Linux and the various prerequisite software for Asterisk and FreePBX then it is the recommended installation method. But even for experts it can be a great time saver.
The FreePBX distribution is appropriate if you are doing a completely fresh server installation. It is not appropriate if you already have a server to which you want to add Asterisk and FreePBX.