if you're cutting straight strips ...
if the selvages are to one side, the you are cutting "up" the length of the fabric. (warp) this is the way i prefer to cut if i'm doing strip piecing (sewing lots of long strips together to cut apart later). they don't stretch as much while i'm sewing them together, and i have a wee bit of stretch after they're cut apart. that comes in handy if i need to ease something to fit.
if the selvages are to the top, then you are cutting across the width of fabric (woof/weft). i prefer to cut this way when i'm going to cut the strips into triangles. just because ... :lol: