It depends on the game whether they will work better without a CD. Older games tended to leave large files on the CD to minimize hard drive space requirements, so could benefit from copying those files to the hard drive and changing a registry entry or configuration file (where possible). DD only checks the CD on startup and for the blessing ceremony and end game videos, so bypassing the CD would only really help if your optical drive is noisy and Windows decides to spin it up periodically.
With the latest
patch installed, disabling the intro videos (see
this topic) will eliminate the CD check on startup, but you will still need the play CD for the blessing ceremony and end video.