Alice owns the patent for a blood pressure measurement device consisting of three elements:
A) a sensor
B) a particular signal processing circuit (the juice of the novel and unobvious functionality)
C) a display
Shortly after the patent is granted, Alice realizes that monitoring one of the signals already available inside element B would allow to obtain additional diagnostic informations, besides blood pressure, which are on their own useful and unobvious. A key point is that said signal is available if and only if elements A, B, and C, are combined together exactly as disclosed in Alice patent. Now, here are some considerations that would appear "common sense" to me:
Alice is afraid that Bob, her strongest competitor on the market, also realizes this possibility and might perhaps succeed in filing for a patent on the novel functionality/use of her patent before she had any chance to do it herself.
But in this case, in order to manufacture and sell such a product, would Bob need to obtain permission from Alice to use her patent? (e.g.: via a license Agreement, which Alice is anyway unlikely to find interesting).
Though, by filing for said "enhanced" blood pressure monitor, the most likely purpose of Bob is simply to prevent that Alice could manufacture and sell it herself, further etching away Bob's market share.
What about if Alice, upon realising the possibility for said additional functionality/use, quickly advertises it in her company's web site (article in the technical blog section, preliminary datasheet for the "enhanced" product, etc.), and this before Bob has had the time to file for a patent. Would the practical result be that only Alice can manufacture and market also the "enhanced" blood pressure monitor? this because her valid patent is anyway needed also for the "enhanced" product, which, after her public disclosure of said additional functionality/use, can no longer be patented by Bob (or any other competitor, for that matter). Compared with filing for a Continuation-In-Part patent, wouldn't this approach represent a much simpler, faster, and lower cost solution for Alice, while featuring practically the same advantages in terms of legal protection of her product IP?
Though the above conclusions appear reasonable to me, I am not at all sure about possible hidden pitfalls.