Ripping fabric is not always a good idea. For one thing, ripping damages fabric up to 2 inches away from the rip. Some of this damage is microscopic, meaning you cannot see it unless you examine the fabric under a microscope. After ripping, it's a good idea to slice off at least 1 inch of fabric so you are not sewing seams on damaged fabric.
Ripping along the lengthwise grain is not as bad as ripping along the crosswise grain. There is not as much distortion and damage along the lengthwise grain. That is why I will rip fabric when I need long pieces for borders (although I make the strip wider and still trim the ripped edges to get rid of any damage before using the pieces).
Straight-of-grain is really important in dressmaking because grain affects how the fabric drapes on the body. It has a different role in quilting, in that grain primarily affects edges -- and how much handling an edge can take before it becomes distorted. A bias edge, for example, will stretch out of shape much more easily than an on-grain edge when piecing. A bias edge is preferable for turned-under applique because it will turn under more easily on a curve than a straight-grain will.
Just sayin'.........