I don't know that it's *that* comon and there are things that your midwife can do during the birth to reduce the likelihood.
I had an episiotomy due to a forceps delivery. It healed up ok within a few weeks, but for me the scar tissue was very sensitive for a long time. Generally, natural tears heal up quicker and better than cuts, so I wouldn't opt for a cut 'just in case'. And, most tears are relatively minor, like Arimeh's.
I've been cut and definitely want a natural birth (with risk of tearing) - I reckon having my abdomen cut open would be worse.

Try to relax. Have you spoken to any midwives about your fears - they can probably put your mind at ease, talking about likelihoods, management plans etc. Or even a good private ante-natal class could be helpful.
All the best for your upcoming birth