Yes, I rip mine to straighten the grain. Fabric is woven with it like you would see in a weaving loom.
First, I pull it from corner to corner to help straighten, then if still not straight, I rip it to get it straight.
The reason this is important to me, is because as your projects are completed, the corners will all match and you won't have to worry about seeing corners that don't match.
If the fabric is of the kind that ripping isn't possible, I pull a thread.
All of these statements I learned from my Mom, who was quite a seamstress, and also from my h.s. sewing teacher, and more recently from our guild.
Mariah