What is the difference between “Profile Picture” and “Web Chat Icon Picture”?

What is the difference between “Profile Picture” and “Web Chat Icon Picture”?

"Profile Picture" is the image displayed next to the messaging bubbles and the Bot Name.
"Web Chat Icon Picture" is the image displayed on the website and you can click it to open up the chatroom window.

Please see the related documentation here and set up the profile picture and webchat icon picture here.