Informal playtesting is when you invite your friends over for a fun game night. This type of testing gives you fast feedback right away. It helps you find big problems in the game and can also inspire new ideas. For example, if a friend has a hard time getting through a level, you can change the difficulty right then and there.

On the other hand, formal playtesting is more organized. It's like a workshop where you have set times to play and collect information. After playing, players fill out surveys to share their thoughts. This method uses data to help make smart choices. It improves the gameplay and makes the experience better for everyone. Overall, it helps in making changes and updates to the game more smoothly.