Do the Time or Pay the Fine?

A guy seated next to me on the F train was talking rather loudly to his friend across the aisle about going to court and being given the choice to do 20 days in jail or pay a fine of $680.  I don't know what kind of crime he had committed, but it must not have been too serious given that he had a choice whether to do time or pay a fine.  I'm sure most folks would choose to just pay the fine.  However, maybe a little time behind bars would help a person to get it together mentally.  Personally, as someone who is terribly claustrophobic, I doubt I'd choose to do the time, but if I didn't have this phobia, I'd probably do the time and try to use those twenty days of incarceration to reflect on what I'd done and how I was going to work to improve my life once I got out.