According to the scriptures, there is a transition state that people experience between the moment of death and the new birth. So often what you see in Thailand, after someone has died, is a lot of people doing a lot of chanting with the intention of dedicating the merit they make from that beneficial action in the deceased person's name. This is so that if the person is in transition, if they are still there, around, not going on to their next life, that their mind may feel gladdened, rather than pulled back by other peoples grief or wish for them to return.
According to the teachings, during the period soon after a person's death, showing a lot of grief and sorrow and crying could upset the person from going on to their next life. Because of this Buddhist teachings, my father's death, I was very, very careful when I arrived at his home where he died. He had a hobby farm, ten acres and he loved his gardens. So I was very careful with my own emotions and wanted to think of him during that time. So I went around his property thinking that maybe he was still around, because he had a strong attachment to his gardens, and I kept on saying, "Don't worry, I'll take care of Mum, no problems." He lived a good lifestyle. I talked aloud about all the nice and wonderful things he had done in his life and I would say , "It's ok you can go on, have a nice next life," with the intention of easing the fears that he may have that my mother would suffer without him.
I tried to just think of him, trying not to get into selfish thoughts, instead trying to think of him and my mother so that I wasn't absorbed in my own grief, or sense of loss. I used the Dhamma at that time. I reflected on the universality of death, so that I could accept it, and have more equanimity with the arising of any unbeneficial thoughts that came. Any unbeneficial thoughts that did arise I was able to transform them fairly easily due to my compassion and concern for both my father and my mother. And I did a lot of Compassion/Lovingkindness and let my father in some of these Compassion/Lovingkindness meditations, to wish him well wherever he was. So I believe, certainly at the transition time, that Compassion/Lovingkindness meditations done for the deceased person would have a great effect.