I went to see my Father, out of curiosity, at 16. By 'accident' I'd seen my Grandad, after death at 15. I was in the hospital supporting my Nan when he died. It helped, I'd seen him fighting for his life.
I worked in end of life care.
I tend to be the first one that goes to see any relatives laid out. I then prepare the others.
When it hasn't looked like them, I've taken a photo, from a distance, if they want that, to make up their minds.
In the case of my Mother and Grandad there was a delay and they no longer looked like themselves. My DDs, in my Mother's case decided against going to see her, my Sister went once and didn't feel that it done her any good.
Personally, it helps me with the grieving process. I sat daily (8 days) with my DH.
A good undertaker, especially with someone younger will request a picture that the person, arranging the funeral, or the deceased, particularly liked. So they get the hair etc as right as possible. They do their best.
If my eldest DD is unsure, she always asks someone whose seen the person.