A viewing provides family and friends with a chance to express personal thoughts, talk to the deceased and maybe just hold their hand. For some, it can be a time to deal with anything unfinished.
If the deceased struggled in life or suffered from a long-term or devastating illness, a viewing can assure family and friends that the person is now at peace.
A viewing can also help some people move through their grieving process. It allows families to really acknowledge that the person has died, so they can come to terms with the reality and finality of death.
A viewing can be particularly beneficial if the death was sudden or unexpected.