A Sale Agreement, essentially captures the terms and conditions based on which this property will eventually get sold to the buyer. Whereas, the Sale Deed is the document which actually transfers the ownership of the property to the buyer. Sale Deed is absolutely mandatory and has to be registered in the Sub-registrar office. A Sale Agreement on the other hand is not mandatory but always recommended by competent lawyers so that interest of both the parties can be protected in case the deal does not go through.