If you have a lot of personal files (like I do), it may also be advantageous to short-stroke your HDD either by shrinking your C:\ partition and moving your personal files to another partition, or simply moving them to another HDD (and leave the C:\ partition full size). If you don't
have a lot of personal files (i.e. you've got GBs or even TBs of video games, but very little personal files) there is no advantage at all to shrinking C:\. Definitely don't install those programs or games on another partition of the C:\ HDD, because this will force frequent seeking between those two partitions.
A defragmenter like MyDefrag will effectively short-stroke your HDD by moving frequently accessed system files and program files to the beginning of the drive, with program and game resource data (in order) following, with infrequently accessed data like installers/uninstallers/service pack uninstallation files/help files and the like, last, where the HDD's read speed is slower.