Tradition and purpose of prostration practice

In the triratna Buddhist community (who I practice with) there is a prostrations practice for those going through the ordination process. I'm sure we have taken this practice from another tradition.I'm fairly certain it is Tibetan but can anyone give details of the exact place in the Tibetan practice this comes from and also what is the purpose of this practice. How does it fit into the system of practice and what effects this practice has on the practicioner.