Then what 's the purpose of this deposit

I am not trying to argure with you, jsut there is something I don't understand. I know that if certain contigiency that is in the offer could not be met, the buyer can walk out with his deposit. No question asked. But if every contigiency is met,then
the buyer has to go on with the contract, otherwise he or she will lose the deposit, right? If things happen as you said, what is the use of deposit?

Please clarify. Thanks