Reason Behind the 48-hour Parking Rule

[wonkywheels.livejournal.com]

There has been some talk in this community about the 48-hour parking rule. Can someone explain the rationale behind this law? I have a car, but I take the "T" or ride my bike to work, so it doesn't make sense to me to have to move my car for no reason. I understand the need to move my car for street-sweeping, but this 48-hour thing doesn't seem to have a basis.