A date without a deposit is an intention. Deposit, deadline and cancellation terms written on the same job avoid the most expensive gap in this business: a Saturday held for months and released in the last week.
One date carries the kitchen, the technical crew, the staff and the suppliers. Putting them on a single schedule is the difference between a smooth run and four phone calls at eight in the morning.
The final headcount arrives late and changes everything: catering, staffing, layout. Fixed with a deadline on the job, the difference stops coming out of your margin.