My thoughts on Quicktime....
A computer novice needs to be careful about installing the full version of Quicktime, it can easily overwrite all your video and audio file associations if you don’t use the “custom” install. You may not want your music files (mp3’s, wav’s etc.) to play through Quicktime.
In addition, there can be risks with any software installation, but I know from experience that the full version of Quicktime CAN have annoying virus like side effects and can also open you up to outside attackers if you’re not diligent with virus, adware, and malware protection. There are processes that can run in the background which slows your computer and it can be hard to fully uninstall Quicktime if you’re a novice computer user as well.
There is a Quicktime Alternative that can be downloaded that allows you to avoid downloading the entire program, but it may not have the functionality you are looking for. Google Quicktime Alternative for more information.
You may do fine with the full version of Quicktime, just be cautious.