A great deal of information regarding on-street parking in Sydney is available here.
Many parking spots within the CBD act as loading zones throughout working hours. Some cars used by people in these loading zones are just regular consumer vehicles so it's very easy to see other cars parked somewhere and misread signs, resulting in a loading zone infringement ticket.
Tow Away Zones
Vehicles illegally parked within this area of the CBD are much more likely to be towed away (compared to receiving a parking infringement fine).
To keep the city centre moving during changes to the bus network from Sunday 4 October 2015 and light rail construction, Roads and Maritime Services and Transport for NSW have introduced several changes to parking restrictions and tow-away zones. More information regarding this can be found here.