PROS OF A CHILD THEME
You can change the styling of a parent theme without changing the actual parent theme template. You can create a child theme and then customize that according to your needs and interest. It helps you make small changes in the parent theme easily and also retain the original theme as unchanged or unedited.
You will not lose your customizations if you update the parent theme as they are now saved in the child theme. Earlier, when we used to update the parent theme all our customizations would vanish. So, no more worrying about losing changes in case you update the parent theme.
GOOD FOR BEGINNERS
If you are a developer and learning to create WordPress themes, then child theme can help you save your time and learn stuff easily as it doesn’t contain tons of files but has only two files. This makes your work easy. Also as the child theme doesn’t have many files, it helps in debugging process as you don’t have to search much.
CONS of A CHILD THEME
You will have to learn the parent theme first to work on the child theme and that often requires a lot of time. So it’s not a one-day task and it will require a lot of time investment. However, once you learn the parent theme and its functionality, the rest of the process becomes easy for you.
With some themes, the problem is if the parent theme is dropped by the developer or a feature is removed, it will affect the child theme as well. However, if your theme is open source, you can continue to work on it even after the parent theme is dropped by the developer.