The Best mode requirement is one of the three written description requirement found in section 35 U.S.C. 112, the other two are the enablement requirement and written description requirement. The best mode requirement still exists through American Invent Act, has largely removed any preference relating to the claimed invention. The Best Mode Requirement historically created a statutory bargained for exchange between the patentee and the people. In exchange for the patent, which gives patentee the right to exclude others from practicing the claimed invention for a certain time period, the public receives detailed knowledge of the invention. The written description requirement essentially requires the patent to define the metes and bound invention and the enablement requirement mandates that the patent explains how to both make and use the invention so that one of relevant skill in the art would be able to make and use the invention without undue experimentation. Best mode goes one step further. In addition to defining the metes and bounds in a way that explain how to make and use the invention, it is necessary for the inventor to also disclose any preferences that pertain to the claimed invention.
The Best Mode Requirement was a safeguard against the desire on part of some inventors to obtain patent protection without making as full disclosure as required by the statute. Failure to disclose the best mode of the claimed invention was grounds for finding a claim at the issue invalid. with the enactment of AIA, the best mode requirement is largely gutted. Although the best mode requirement remains in the statute and needs to be satisfied at the time the patent application is filed, the failure to disclose the best mode is no longer a basis on which any claim of an issued patent may be invalidated or otherwise unenforceable.
Why would Congress keep the best mode requirement if they were going to render it useless insofar as determining validity and priority claims? Why not eliminate the best mode requirement from 35 USC 112
The United Patent and Trademark Office has noticed that while the lack of the best mode disclosure cannot be used to invalidate a claim or to prevent a claim of priority, the disclosure of the best mode remains one of the patentability requirements pursuant to 35 U.S.C 112. The 35 USC 112, still requires the disclosure of the best mode known to the inventor so that legally applicant is still required to disclose the best mode even though the failure to do so will not validate an otherwise valid claim. Of course one could legitimately ask the viability of USPTO continuing to consider the best mode given that it is the purely subjective test in the first part, which seeks to determine what inventor actually preferred. The patent examiner would only in the most extremely rare cases ever be privy to information relating to the subjective preference of the inventor. Still, it is theoretically possible in that rare case, and if the patent examiner is made aware of preferences held by the inventor the claims implicated should not be granted. Thus, there is a distinction between issued patent claims and claims not yet issued when it comes to best mode.
Playing fast and loose with best mode requirement does not make a lot of sense at least not for most inventors. Perhaps some inventors believe it to be advantageous to withhold information about preferences, but if you withhold information and do not include it in your patent application then it will not be a part of your invention. In an other word, withholding the best mode not only calls into question whether you have satisfied the best mode requirement but will call into question whether your written description has fully described the complete invention.
If you have any preference why would you now want to own that preference?
Most Inventors should want to disclose the best mode of their invention that is not optimal and allow the optimal version of the invention to remain unprotected. Generally speaking, disclosing the best mode of their invention so that they can own the right associated with what they prefer.