Some trivia game shows ask questions to one contestant at a time instead of pitting them against each other directly with a buzzer. For example, Alice will answer a set of questions, and then Bob will answer a set afterwards. The problem with this is, if Alice and Bob are asked different questions, it doesn't feel fair, and if they are asked the same questions, then Bob will know the questions ahead of time when they're asked to Alice. As to why they couldn't just put Bob backstage: a sound-proof booth is just cooler.