Those people who, while they were alive, never acknowledged the reality of life after death or were only attached to material possessions roam about in the lower regions of the astral plane for a long time when they leave earth. They are wandering souls, who suffer, and although spirits of light try to help them, they still cannot break their attachments.
Those, on the other hand, who have cherished a great spiritual ideal during their life rapidly leave their body and fly away to the sublime regions, where they swim in light and joy.
From there, they can send blessings to all those they have left below, to help and protect them. But they never come back to visit them, the way many people imagine.
From the moment they leave their body, they are a long way from earth and do not come down again.