When made public, your interests and favourite game are viewable to other players who look at your profile in the community chat room. It's a fun way to show other people who you are and what you like to do so.
Here's how to toggle your profile page between public and private:
To start off, click 'My Account' at the top-right corner of your screen and then select 'My Profile":
At the top of the page you will see either Private or Public. This indicates your current preference. To change it, you may simply click on the option you want and it will automatically update: