I wash my fabric, then rip it to get it on the straight of grain, iron, then I rotary cut from there because it is much easier to get straight lines and the fabric is not skewed. Sometimes I will rip off a piece a bit larger, say about 1/2 yard, selvedge to selvedge, then I can fold twice and rotary cut keeping the fabric straight and into smaller strips with little waste.
I always rip my borders along the length of the fabric and it's perfect every time.
I've had quality fabric that has been cut and skewed very badly so I would lose up to three inches on each side when fixing the grain. Ripping avoids this completely.
I haven't had my fabric ripped when I purchase it, it's always cut. Maybe I should be asking them to rip it!
Diane