look at the back of the fabric.
see if the print follows one of the threads or wanders off
if it wandered off, it was printed off-grain and the options are
- do not use the fabric
- cut it on grain and have the print look wonky
- cut it to follow the print and ignore the grain lines
i think grain line matters - especially on the outside edges of a block - because straight of grain is,less stretchy than a bias edge. generally speaking, crosswise grain is stretchier than lengthwuse grain.
doreen speckmann suggesting cutting sashing on the crosswise grain because it was easier to "fudge" if one needed to ease in a slightly larger block.