הלכה על יומא 106:12

Upon the conclusion of the prayers of supplication, one recites Yihyu le-ratzon again and takes three steps backward, thereby departing the King’s presence. The Sages say that if one prays and does not depart from the Amida properly by taking three steps back and saying “Oseh shalom…,” it would have been better not to have prayed at all (Yoma 53b). One who does not take leave properly demonstrates that she does not understand that she was standing before the Almighty King, and she thus demeans prayer.

After taking three steps backwards, one must remain standing in that place. She may not immediately return to where she prayed the Amida, for if she does, she resembles a dog that returns to its vomit (Yoma 53b), since if she returns to stand before the King without any good reason, having just taken leave from Him, she shows that she did not understand that she was standing before the King and departed His presence. Her behavior is thus considered disgraceful. Some people compound this error by returning to their initial stance and then lifting their heels slightly, as one does when reciting Kedusha. There is no reason at all to do so.