Why are follow rest and steady test used lathe?

At the time of turning long bars the follow rest and steady rest are used.

Follow rest is used near to the tool at the back side of the job ie bar and it moves along with the tool such that it gives support to the job so that the job does not get deflected due to the tool preacher.

Steady rest is used to give support to the job in the middle or at a end so that the job should not get bend.