If your one who uses iTunes then you have Quicktime installed on your computer. The Quicktime plugin is nice for sites that require Quicktime but as an overall player there are better options like VLC Player. There are certain products that do require Quicktime and won't detect the Quicktime Alternatives as Quicktime anymore. iTunes is one of them that no longer recognizes Quicktime Alternatives as Quicktime itself being installed.

It's one of those you probably need it even if you don't want it type things. So you install it because it's better safe than sorry.

I would never recommend Quicktime except for the fact a lot of things call for it. You can see if the alternatives work for you then only install Quicktime if needed.