Sometimes you can get one type of media easier or cheaper then the other.
Also it's nice to be able to support all posibilities, your stuff might work with one type great but you families stuff might want another.
I have gear that can support both types, but not always, depending on what I'm burning, the file types, and the method used.
And a lot of us just like to have the latest toys to play with anyways if we can afford it
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