Theft of information from the employer

Have you ever had cases when:

• Have you or your colleague quit and copied all the employer's data (documentation, databases, customer contacts, employee contacts [so you can find them if you need employees])?
• Have you or your colleague sitting at home after being fired used this information for any purpose?
• Have you or your colleague tried to sell this information "on the side" or, on its basis, to open your own business, competing with the previous employer?

If you can not talk about yourself - say "about a friend."
From what I saw:

• The data is copied to a flash drive or disk by half. This may be documentation, source code, etc.
• This information was viewed by a person a couple of times maximum (except for the cases when the available documents were used as templates for new ones).
• Nobody took advantage of the information for the purposes unattainable for the previous employer - partly due to the lack of understanding of how this information and knowledge can be commercialized.

What examples do you have?