What are dynamic modules and widgets?
When the cache is created, the page is anonymized, that means it is displayed without any information about the visitor displaying the page.
Modules that display content relative to the current visitor can be marked as dynamic, that means the content will be refreshed (replaced) by a background request (Ajax) in the browser that will carry the context of the current visitor.
If you check the option "Display nothing in cache" then the module will not be called to display its content in this hook during the creation of the cache. However, the content will be displayed as other dynamic modules (with a background request (Ajax)).