If an alcoholic stops drinking, they go through a period of suffering. Watching someone go through that is rough and you would like to do all you can to ease their suffering. What a person should never do is give them a drink to ease the suffering because it only prolongs the suffering.
Similarly, watching someone who lost a loved one, suffer the hole that is left in their life is difficult. You want to do all you can to ease their suffering. Letting someone go, emotionally is a difficult process but eventually, they have to come to terms with the fact that they are gone. Not only aiding in convincing that person that their loved one is still hanging around, but is also conscious and communicating with them will stall acceptance and prolong the healing process.