I serge the ends (overcast with zigzag if serger not available) - then soak in hot water - and then wash and dry gently.
The ONLY time I will rip/tear the ends off (to straighten or to get a piece off a longer length)is if I am doing something where I know that I can lose up to an inch and a half - and sometimes more - (on each side of the tear) due to damage caused by the tearing.
If I am short of fabric and straight of grain is very important - I will pull a thread - tedious, but it does not cause a lot of damage to the surrounding fabric.