Having a chat feature on your website (commonly called 'live chat') is useful when helping your users overcome any difficulties they are having. You can pop up a little chat window in the page and ask if they need any help finding what they need. This can be especially useful on large commerce sites where users might get stuck looking for things.
The addition of a chatbot also allows you to automatically answer some of more common questions. For example, if a user asks where they can find the delivery and returns policy then a chatbot can automatically respond with a response. These rules can get more complicated, but it depends on what you instruct the bot to answer to.