Preparing Fabric for Rotary Cutting
All fabric should be well pressed before cutting. Some fabrics can be difficult to achieve a good pressed look after washing, just keep in mind that as long as it is flat and will cut accurately then the tiny difficult creases may eventually be removed simply as a result of the many, many times that the iron will be used during the piecing process.
Many people are firm believers in the necessity to wash all fabrics prior to using them for quilting. The main two reasons for this is that it's an opportunity to rid the fabrics of excess dyes and starches from the manufacturing process, and to allow for any shrinkage that may occur. This is especially true when using darker blues or burgundy fabrics. On the other hand some quilters love the crisp feel of new fabrics and prefer to work with unwashed fabrics.
A warning is needed, if the quilt is to be a wall hanging and maybe not ever need to be laundered then it may be worth the gamble to not wash the fabrics. On the other hand, if the quilt is to be used on the kids bed and likely to require washing then maybe washing the fabrics before you start piecing will save a lot of heartache down the track. There is nothing worse than your pride and joy emerging for the laundry out of shape and with colour runs!