If you retain only ONE THING after taking the Patent Bar, remember this. You can't insert "new matter" (aka new information) into your patent application once you submit it.
This is usually why patent applications are so detailed and long. Applicants/inventors/patent attorneys try to include every possible thing you can think of in the specification so that the application claims are well supported during patent prosecution.
But if you're at a point in the patent prosecution where you need to include new information, you can either do one of two things: 1) file another patent application and include the new information; or 2) file a continuation-in-part (CIP) application.
I've had some discussions with my coworkers on which is better. Personally, I'm not sure yet.
Some people want to file a CIP application. This is an application where you can include everything you've already included in your original application PLUS new information. All of the information you've previously disclosed in the original application receives the priority date or the filing date of the original application. Everything new, however, receives the filing date of the CIP application.
Some people just want to file a new application, which is sort of a more simple option of the two. New application gives you a new filing date, and that's pretty much it. New applications seem to make sense for some people because filing a CIP application can basically give you a shorter term of patent protection because a patent protection term lasts for 20 years from the date of your filing. That means a new application will basically reset that 20 year clock, whereas the 20 year clock for the CIP application started from the date of the original filing.
Sometimes the difference in time is only 2 to 3 years, which may not be a big deal for most people. But it may matter to some. Also, some clients lean toward filing a CIP application because it can cost them less legal fees.
I'll have to see which one tends to be more successful in the future.