In other words, an assignment clause allows the buyer of a home to sell the place before they take possession of it. In Ontario, assignments are more common in pre-built homes and condos than on re-sale properties, but they are possible on any type of trade.
Under property law, assignment typically arises in landlord-tenant situations. For example, A might be renting from landlord B but wants to another party (C) to take over the property. In this scenario, A might be able to choose between assigning and subleasing the property to C.