Certain loans and contracts can prevent you from being able to sell something without the lien being lifted.

For example, if you have a mortgage on a house, or in some cases if you're paying a contractor to do renovations, you can't just sell the house out from underneath them and run with the cash. Someone "buying" shit with a lien on it could outright lose it in some circumstances (though it would be pretty hard to get there for land because the process is so protracted).