What are the positive effects of euthanasia?
In both human and animal euthanasia, the positive aspects are a painless death that, in many cases, brings an end to severe chronic pain and suffering. The person dying can sometimes say goodbye, and family/friends for both humans and animals can say goodbye as well. Particularly in animal euthanasia, the animal can be put down in a comfortable environment such as home or a favorite blanket to help comfort the animal during the process.
Euthanasia is the act or practice of ending the life of a person either by lethal injection or the suspension of medical treatment. Because of this, many view euthanasia as simply bringing relief by alleviating pain and suffering. The word has also been applied to situations when a decision is made to refrain from exercising "heroic" measures in an end-of-life situation. The positive effect of euthanasia is that the person affected by it will be relieved from pain and/or suffering. The negative effects of euthanasia is that no one knows what is in future. You may succeed to be recovered from pain and suffering. So, you lose your life without a reason. The second negative effect is that euthanasia is like committing suicide; something that is sinful in all God religions.
The primary positive effects of euthanasia is to limit the further suffering of the person. That is, it is judged that ending the person's life is more helpful to the well-being of the person (i.e. more humane) than requiring the person to continue to wait for a "natural" death. It can also be seen as allowing a person to have a measure of control over their destiny, rather than be subject to the whims of their particular ailment or condition. Note that the above generally only apply to self-directed euthanasia - that is, euthanasia conducted at the sole direction of the person being euthanized, with no meaningful outside inducement. Euthanasia committed at the direction of a 3rd party is almost universally seen as evil, with no real redeeming value. What are known as "mercy killings" are properly considered of a different nature than euthanasia, despite the occasional mis-labeling in the popular press (that is, occasionally, actions which should be properly termed euthanasia are labeled a mercy killing, and vice versa).
Euthanasia can sometimes be seen as a way out for terminally ill patients, obviously. Euthanasia is usually requested by the patient because they are in too much pain, or because the medical bills would be so high that their family cannot support them. Some psychological effects of euthanasia, would obviously be grief, as with every death that occurs. But, a sense of guilt could also be felt as you helped kill a loved one.