What Are the Security Risks Associated With Not Logging Out Of Sensitive Websites?

Assuming strong passwords and two-factor authentication are in place, how important is it to always sign out from a website such as Apple, amazon, a bank or some other website that could be used to steal money from you?
I would like to know if my sensitive accounts that move money could be compromised is I fail to log out. Some accounts like amazon, I may enter several times a day. It would be more convenient not to log in each time.
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Steve