It is discouraged, difficult, unnecessary, and illegal in some locations.
The Xbox has a specific function: Non-booting or non-reading from CDs and DVD-Rs as a method of game copy protection. Also, the Xbox is said to use a different DVD file system (instead of UDF). It has been theorized that the discs have a second partition that is read from the outside in (opposite current standards thus making the second partition unreadable in PC DVD drives) which give the tracks the appearance that the disc was spun backwards during manufacture. The Xbox 360 copy protection functions by requesting the DVD drive compute the angular distance between specific data sectors on the disc. A duplicated DVD will return different values than a pressed original would.
This is meant to keep users from copying disks. It is, in a nutshell, made so that you can't use CD-R's and need disks that were manufactured to have special layouts of sectors upon the physical surface. This is done as such copies are not generally legal. Also, the fact that a proprietary filesystem is used means that discs cannot be read using normal drives and filesystem utilities.
Legal disclaimer: This is not meant to be legal advice. The author of this answer and Stack Exchange, Inc will not be responsible for any damages, incidental, or consequential, that may arise due to the use of these guidelines. These guidelines are based on US laws and regulations. Laws and regulations in your area may differ so check with a lawyer or local authorities.