It depends on a person's reason for writing the letter, and the contents of the letter. It should serve the purposes of the writer. Any convenience it causes for the JWs should be purely coincidental.
It's been said that writing a letter is "following their rules". Submitting to their cat-and-mouse game can also be called "playing by their rules".
In my opinion, if you have to hide anything from them out of fear of reprisals, then you are playing their game - acknowledging their authority.
Granted, there are often valid reasons for doing so. Some try to fade so they can maintain family relationships. Some for financial reasons. I've met many ex-jws who have done that, but even years later they still feel the need to hide who they are. And yes, some even attend meetings so they can keep their families. Those of us who come out and tell them straight to get the fuck out of our lives immediately gain our freedom but suffer other consequences. Each person has to weigh the pros and cons in their own situation.
In my own case, I wasted what should have been the best years of my life in the cult, and I wasn't prepared to waste a minute more. I was being watched. My ex-wife was subjected to a car chase by elders who mistakenly thought I was driving. (They aborted the chase when they pulled up beside the vehicle and saw her). They were constantly phoning and knocking on my door. I wrote them a letter and told them to cease their harassment and to cease trespassing on my property, or there would be legal consequences. They immediately complied without question.
I did what was best for me, and I have no regrets.
W