The purpose of bail is to guarantee the arrestee's appearance in court. Bail is not a fine and it has no connection with the guilt or innocence of the person arrested. It will not be used as a penalty if the person is found guilty. You can consider bail as a form of insurance for the court.

How Is A Bail Bonds Cost Determined?
In California, the is something called a bail schedule. The arresting officer assigns a violation code to the defendant's wrong doing. There are two different code schedules, one for misdemeanors and one for felonies. Say the officer has arrested an individual on a PC 422 charge. According to the bail bonds schedule this is a criminal threat and carries a cost of $40,000.
The defendant has a choice of either staying in jail or posting $40,000 bail bonds. The defendant can either provide the court with $40,000 in cash or getting someone else to put up that amount of money for the court. This is where the bail bonds company comes in to play. The defendant gives the bail bonds company 10% of the overall bail bonds cost and the bail bonds company will post what's called a bond. So now the bail bonds company is responsible for the $40,000 bail bonds that the defendant has and hopefully the bail bonds company also has an indemnitor.
An Indemnitor is a third party who is taking the resonsibility of the $40,000 bail bonds. The indemnitor is usually a friend, parent, or lawyer. They sign the papers vouching for the defendant to return to all of their court dates.