Why you should be logged out of email, Instagram, Windows, and all your accounts before you turn off your computer.
Your own or company's data can be stolen via your account.
Your email, Instagram, or maybe even bank accounts might be accessible by others.
Your browser's cookies can be copied to access your accounts from other computers.
Your accounts can be used to spread spam, phishing, or even viruses.
Your email can be used to create or access other dummies accounts or even used for criminal activities under your name.
If you are using Brave or Edge browser, you can set to clear cookies on exit and it will automatically logged you out of all your accounts.
Refs.
https://www.computerhope.com/issues/ch001120.htm
https://www.fbi.gov/how-we-can-help-you/scams-and-safety/common-frauds-and-scams/business-email-compromise
https://www.cybersecurity-insiders.com/can-failing-to-log-out-from-online-accounts-pose-a-cybersecurity-threat/