[Pete1210]

This article found significant decrease in load times if you install the game to the hard drive.
Halo: Reach load comparison, Installed vs Not installed

Quote:

Installed: Opening Mission: 8.1 seconds. Not Installed: Opening Mission: 21.4 seconds. Installed: Firefight: 21.6 seconds. Not Installed: Firefight: 45.1 seconds. Installed: Custom Game Load: 9.7 seconds. Not Installed: Custom Game Load: 28.7 seconds.