Analog transfer is less reliable. In other words, you can be less sure that the signal on one end of the cable will be identical at the other end of the cable.

I came across the following enlightening forum post a couple weeks ago. It talks about HDMI cables, but the lesson applies to all cables.

http://boardsus.playstation.com/playstation/board/message?board.id=ps3&message.id=828972