* Insurance: Your insurance may be invalid if the vehicle isn't properly registered and plated.
* Inspection: If the car is unregistered, it likely hasn't passed inspection, which is required in Massachusetts.
* Police scrutiny: If the police see a car without plates, even on private property, they may investigate. They might suspect it's stolen or involved in illegal activity.
* HOA regulations: If you live in a community with a homeowner's association, they may have rules about the appearance of vehicles on the property, including the presence of license plates.
In short, while technically you might be able to park it, it's not advisable. Getting the car properly registered and plated is the best course of action to avoid any potential issues.