The Apply Updates dialog appears when you refresh, register, or save the type library if you have selected Display updates before refreshing in the ToolsOptionsType Library page (which is not checked off by default ). 

Without this option, the Type Library Editor automatically updates the sources of the associated object when you make changes in the editor. With this option, you have a chance to veto the proposed changes when you attempt to refresh, save, or register the type library. 

The Apply Updates dialog will warn you about potential errors, and will insert TODO comments in your source file. For example, if you rename an event by mistake, you will get a warning in your source file that looks like this:

Because of the presence of instance variables in your implementation file,
Delphi was not able to update the file to reflect the change in your event
interface name. As Delphi has updated the type library for you, however, you
must update the implementation file by hand.

You will also get a TODO comment in your source file immediately above it.