Two parties want the same Friday night and you're trading emails for days while both dates sit unconfirmed.
Clients see your open dates and lock theirs with a deposit, reducing the back-and-forth around competing inquiries. You hold a date on a handshake, turn down another gig, then the first client books someone cheaper.
Hold the night after the deposit is collected, so the confirmed booking includes money down before you decline another gig. Contracts unsigned and the final balance unpaid until you're loading gear into the venue.
Collect the deposit with the booking, then email a card invoice for the final balance and track its status from the event record.