From what I understand about the way fabric is woven, to rip it from selvage edge to selvage edge does not stretch it as much as ripping the selvage edge longways. I have cut fabric "longways" to avoid seams in making valences and they began sagging (not a pretty sight, believe me). I usually fold it so I can cut 4 layers at one time.
When I sew a long seam such as a border, I always pin (which I know is not a popular technique among many quilters). I like the flower head type for all types of sewing.
Sis