I think the backs of Tarot's are only of importance when they are either particularly beautiful or particularly ugly.
A very ugly backing on a Tarot is the Pagan Tarot 2000, which has this really horrible picture of an eye at the centre, with a spider web shape surrounding it and rainbow colour's behind. It's so awful I did consider colouring over the backs with black marker, but I didn't bother as I don't use them that much. I don't like boring backings either, such as the stale brown tartan type backing on the IJJ Swiss. I feel that an unattractive back on a deck is important because it can put you off using them, regardless of the fronts, because it is the back of a deck that makes that first impression upon the person being read for.
An attractive backing on a deck, such as the gorgeous back of the Gilded, is important, because as I said, it makes that first impression, and if this impression is good, it makes one all the more eager to see the fronts. It's all about presentation.
If the backings of a deck are not very attractive or very unappealing, then I don't suppose it matters at all really.
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