I get this question relatively frequently from my clients.
Tearing
Tearing is avoidable by several factors- no 'purple' pushing, pushing in upright positions, allowing tissues to stretch instead of trying to get baby out as fast as you can, perineal support, avoiding epidural, not pushing on your back, and encouraging optimal fetal positioning. All of these things are within our own power as we labor. It's not a guarantee that you won't tear, but you're
significantly less likely to tear.
Tearing is less traumatic to the tissues (usually) as it is more likely to be superficial and not go into the muscle tissues. Now, of course there are exceptions to every scenario. I've seen some nasty tears and tiny episiotomies, and I've seen gigantic episiotomies and no tearing at all. I had a client give birth to a 10#3oz baby girl over an intact perineum, on her back!
Episiotomy
Routine episiotomy is a surgical procedure that is done not because there is a reason, b ut because that is how it is done (like not letting women eat in labor). Who wants surgery they don't need?
Episiotomies are much more likely to cut down into the muscle structure that makes up your pelvic floor. Pelvic floor damage is getting a lot of press lately due to vaginal birth vs. cesarean birth, but episiotomy is an enormous culprit in this condition.
The body prefers to heal a tear rather than a cut, so healing time is usually faster and with less complications when you tear, rather than are cut. Surgeons (OBs are all surgeons) prefer the cut because it is much easier to repair.
Think about this: some docs give episiotomies so that the laboring woman won't tear. The goal should not be to avoid tearing, it should be to avoid any sort of perineal laceration. Whether you tear or are cut, you are still dealing with a laceration, right? I try to educate my clients/students about avoiding a laceration all together, rather than settling with an episiotomy.