An “optimized” Certified PDF document is a Certified PDF with reduced file size.
If you edit and save a Certified PDF document, you may notice that its file size will increase. The reason is obvious: all the changes done in an editing session are stored in the Certified PDF document. So even if you perform actions which would normally reduce the size of your PDF file, such as removing objects or downsampling images, saving the PDF document will increase its file size. And this increase can become significant, depending on the types of actions and the number of editing sessions you do.
If file size is or becomes an issue, you can “optimize” your Certified PDF by using the Save As function of Adobe Acrobat to reduce its file size. You will then still have a Certified PDF document with history information about previous editing sessions, but you will no longer be able to: