While it can be emotionally draining, and even stressful, I think that going to a visitation is a good thing for most people. It gives you the ability to have a bit of closure, so that you can say good-by one last time.
I have to agree with saphir but if you have a history of panic attacks or serious emontional breakdowns then that may be something you want to consider because then no it it may not be mentally healthy.
Personally, for me, I don't like having that memory as my last memory of them. I have no problem believing they are dead though I haven't seen them that way. I didn't see my mom, son , sister, daughter in law dead, but I accidentally saw my dad dead and now that's all I can see in my mind. It's a personal choice and children definitely no.
If you can handle it, yes. The closure is cathartic. My mother died at the age of 40 and I was only 18. I will not share my experience of "viewing" her in the casket however, you never want to regret something you could have done. My condolences.
Yes it is. If you really love the person than you should have your last good bye and knowing that you will se them again. It just gives you this peace. Sometimes it worse not doing it because you will have regrets down the road and that is not healthy :)