i do not trim my torn fabrics, that bruised edge goes into the seam... if you rip it fast, it's fine. and i do rip everything that i put aside for borders... (i rip borders off in 2, 4 and 6 inch widths and store that way because that way i'm not cutting away the length with piecing strips. but when going across, it depends on what i'm gonna do with it... so i do both.. from one end, i rip each strip i need for my strip piecing... but cutting template shapes and making magic squares for HSTs, i do it from the other end, because a small triangle or square cut on the double layer method does not go across the fabric so there is no real reason for them to be PERFECTLY straight, square from the selvedge and fold lines is good enough... i just fold my fabric from the ripped end (because i know that is straight) and then next time i use the end that is correct for that day's method...