In theory, it's hard to understand. But once you've actually suffered a major financial loss due to a wedding cancelation, it starts to make more sense from a business perspective. Let me explain.
Our contract terms have always been to collect 1/3 of the payment at the time of booking. It is a significant amount; and I am making a significant commitment to the client. Doesn’t matter if a “better offer” comes along (or I change my mind, or I win a free trip to Europe, or J.Lo wants me to photograph her 4th wedding) I am committed to the original client and their date. It works both ways, and the non-refundable retainer is the client's way of making that same commitment to me.