CentOS Live CD vs Live DVD download
Most probably the Live DVD contains packages the Live CD does not. Thus, for a one-time investment in a larger medium, and a continuous small increase in boot time each time the Live DVD is loaded, you would have additional built-in functionality as compared to the Live CD.
Additionally, if you were to use the Live medium as an install disc, you would have a "running start" with the DVD when it comes to included functionality.
Unfortunately, the readme for the Live distribution does not list the included packages, and the links to the wiki within the readme have not yet been created.
It looks CentOS lacks proper documentation, but the difference is the different list of pre-installed applications.
Generally, there is no need to download the DVD unless:
- you have a poor home internet connection, but can download the DVD from somewhere else
- you're a bit lazy and prefer to download system with a wide scope of applications ready to use out-of-the-box
If you know exactly what kind of applications you are looking for, using LiveCD and just installing what you really need may be much better solution.