user18029: At the top levels of chess the identity of the coach/assistant is sometimes kept secret.
What are the advantage(s) of this?
I found:

That mystery [second] turned out to be the intensely creative Russian master Daniil Dubov, whose influence on Carlsen would later become clear when he leaned on a specific variation of the Sicilian defense against Caruana.

It seems some advantage is to be gained by surprising an opponent with a variation or opening. Is this correct and are there any other reasons?

user4418: The main function of a second is to provide timely analysis and advice to the principal player, both before and during the match. If the second is being pestered by the chess press because their identity is known then it becomes more difficult for them to do their job properly. It is an added unwanted distraction.
Second, the second will have particular areas of expertise for which they are being employed. The knowledge that the principal is looking for advice in these areas is useful knowledge for the opponent and so keeping this secret is desirable.

18029: <p>At the top levels of chess the identity of the coach/assistant is sometimes kept secret.</p>
<p>What are the advantage(s) of this?</p>
<p>I <a href="https://archive.ph/BhUqn" rel="noreferrer">found</a>:</p>
<blockquote>
<p>That mystery [second] turned out to be the intensely creative Russian master Daniil Dubov, whose influence on Carlsen would later become clear when he leaned on a specific variation of the Sicilian defense against Caruana.</p>
</blockquote>
<p>It seems some advantage is to be gained by surprising an opponent with a variation or opening. Is this correct and are there any other reasons?</p>
 4418: <p>The main function of a second is to provide timely analysis and advice to the principal player, both before and during the match. If the second is being pestered by the chess press because their identity is known then it becomes more difficult for them to do their job properly. It is an added unwanted distraction.</p>
<p>Second, the second will have particular areas of expertise for which they are being employed. The knowledge that the principal is looking for advice in these areas is useful knowledge for the opponent and so keeping this secret is desirable.</p>
