If one works with the directional flow of energy chakras and such, then the hand that is used may be important to that person.
Depending upon the person giving the reading, their beliefs, the person getting the reading and their current flow of energy as well as what the issue may be, such as, are they wanting to STOP something, or are the wanting to OPEN up something, are they giving or receiving? Are they trying to move a blockage or are they trying to build protective boundaries? All these would factor in for some people and would use that to determine the reading ritual.
The use of the Left hand is not like the other silly tarot myths that have no real foundation. It is long practiced that they left hand is the creative out-flowing hand.
I personally am a both-handed person. I write with my right only because that what I was told and taught and that is what I am ‘supposed’ to do. Everything else I do I do with my left hand, so it is natural for me to use my left hand and that is the only reason why I do.