I heard this long time back that one should not immediately turn back after praying, instead take at least 2 or 3 steps back and then turn around. The reason is one should not make their back face the deity immediately after praying. Is this true? If so why?
God is everywhere, but Tirthas, holy places of pilgrimage and temples have a greater manifestation of God then other places. It is because they have been made holy by innumerable visits of pilgrims and holy men and women. The places can sometimes vibrate with holiness. When standing before a human king, the custom has been in many countries to back away from the king so as not to show your backside to the king as it was considered an insult to show your backside instead of your face to the king.
So it is with a murthi in a temple. The murthi is the representation of God. It literally vibrates with God's presence. Why not give the same consideration to the King or Queen of the universe as you would to an earthly king?
Most people show humility before those then consider their superiors. The same courtesy should be shown to God. God will not hate us or get angry if we do not, the humility helps us to learn to love God.