When they crucified people why did they bother to nail or tie down the feet?

Unless the legs were stretched apart like on a Saint Andrews Cross, the legs just hang down so why bother tying or nailing them on to the cross?When they crucified people why did they bother to nail or tie down the feet?
Just a guess, it would be more painfull, all the weight of the body bearing down on already nailed feet, and it would help keep the body from slipping down off the cross.When they crucified people why did they bother to nail or tie down the feet?
The Romans discovered that if you nailed the feet of a person to the cross at a certain angle, it became impossible to exhale without first pushing up on the cross; thus inflicting greater pain and misery for the victim.
As jorst said.When a person was executed on those days it was in public and the more gruesome and painful it was the bigger the deterrent.