Backup and storage
One of my external drives is used for backup with Ghost. The other holds my mp3s. When I have the money to get back into video work, I'll have one for that too.
I disagree with the post discouraging the use of external drives. Why? The Ghost files would fill 2.5 DVDs. My desktop backs up automatically three times a week in the middle of the night. Yes, I back up the Ghost files to DVD occasionally.
The other reason - the mp3s. I have those backed up to DVD as well, but using the DVDs (six of them) to access those files regularly would be a nightmare.
There is no reason not to use external drives. You just have to treat them with the same care and common sense as you do with the rest of your system. The same goes when buying one - don't cut corners to get the largest capacity for the least money.