Why pay a deposit for a wedding planner contract?

Because, a wedding planner will have invest into that wedding. Every wedding is different and unique. I have to travel to see and make arangements with my vendors., often what I am looking for is 6 hours drive time away. Also it is a security deposit, if I invested 3 months into an event, and couple decides to postpone the wedding 2 weeks before the event, my vendors will ask for reimbursment. If I am ordering flowers from Holland for example, I am in big big trouble.