While the NXE's ability to let you install 360 games to your HDD is mostly a good thing (no more disc read errors at my house), it's been revealed that there's a few hiccups. You'd think that copying a game to your 360's hard drive would speed things up. Faster load times, that kind of thing. But in some cases it doesn't. Especially when it comes to Halo 3. Tests have already shown the game runs faster on disc than it does on HDD, and today Bungie have come out and confirmed this. Confirmed it, and explained it.
Basically, the game was programmed to copy map files from the disc to the HDD to speed up load times. If you install the game to the HDD, it copies the files from your HDD to...another part of your HDD, which is a lot slower than a disc-to-HDD transfer.
Why does Halo 3 do this and other games don't? Bungie's Mat Noguchi says "we shipped Halo 3 before Microsoft finalised this particular feature. As a result, we were not able to take advantage of it (or any other potential optimizations we discovered after shipping Halo 3)".
While refusing to rule out the possibility of a patch fixing this issue, Noguchi says "it would be a significant undertaking to try and retroactively patch/update Halo 3 to be optimised to take advantage of the HDD install features of NXE". Especially when, you know. You can still play Halo 3 just fine off the disc. Like you always have.
Halo 3 & NXE [Bungie]