Yeh, if your familiar with the whole 'Xbox 360 Scratches Disks' Phenomenom then you will no why, if not im going to tell you
You move it the disk moves and will scratch against one of the inside components while spinning 100's of times a minute so it totally fux your CD/DVD.. Dont Do It, TheMajor is probably right, But DO NOT try it upside down unless your testing it ona spare disk
Personally i find External a pain in the A*S, It's just gona break, and brteak the cd/dvd inside it assoon as you hit it accidentally. But im a *clumbsy* ( * Sp ? ) person so it might be different for you. LOL.