Yeah, but you actually get better performance if you can trick the game into reading off the hard drive. CD drives are sloooow compared to HDs.
I play Master of Orion 3 (on a somewhat underpowered computer), and the biggest performance drag is the CD - every time it wants to play a new video sample or sound effect, it spins up the CD rom, and the whole game lags waiting for the CD drive to catch up. My CD drive is also kind of noisy, which is annoying... I wish I could trick the game to use a disk image from the HD, it would be much faster, but I haven't been able to figure out how.
As I said, Alpha Centauri on OS 8.6 could be fooled into using a disk image of the game CD, and the performance was much better when I did that.