What is the point of installing a game?
Much like those in your computer, optical drives spin at varying speeds based on the data they're trying to read. It doesn't mean much, and in general should happen more on startup and loading screens. If it gets to be too loud or disruptive, you always have the option to install games to your hard drive. Note you'll still need the disc in the drive, but it will attempt to read data from the hard drive instead of the disc, making it generally faster and quieter.
I generally keep the game that I've been playing the most installed on my xbox and uninstall games I haven't played in a while to keep space free. I appreciate the faster load times and quieter operation, but it is by no means required that you install games to your hard drive.