I am hesitant to press with steam if the fabric has not been pre-washed. The sizing could distort the pieces. Also, if there if a difference in quality (thread count) of the individual pieces. Dry iron is safer. I attended a class with Sally Collins last weekend and she presses with dry iron and then puts a heavy book on the piece until it cools. This really works in keeping the seams flat. I often steam press as the final press when the top is together, especially from the back to halep keep all the seams flatter. I believe many believe dry is safer. I will iron the fabric with steam before cutting. This should help with additional shrinkage of the fabric.