I hate ripping fabric. I always recut the edge because it stretches the weave. With that being said, I do rip if I have a long length on the straight of grain to do. An example would be ripping the edge of the material for long border pieces without having joins. I measure out a good inch more than needed and rip the border part first. This gets the long pieces down to a managable size to recut the edge. This is the one time I like to rip rather than fold. I always worry with folding that much fabric that I will cut the border and open it up to find the dreaded "V" or "dogleg". Go with what feels comfortable to you.