What is the use of the announcement and examination notice of the application for a patent for invention at the substantive stage?

The notice that the application for a patent for invention has entered the substantive examination stage is the intermediate document of the application for a patent for invention, indicating the present stage of the invention patent. The time limit for filing a request for substantive examination of a patent for invention is three years from the date of application. If it is not mentioned within this time limit, it shall be deemed to have been withdrawn and the patent application shall be invalid.