Having been here since 2016, I can tell you there is definitely no such thing as a consensus on usage of content warnings on the fediverse. It's a decentralized network that doesn't belong to any one party, so by definition there is no single culture on it. Different corners have different expectations and customs.
For my part, I've always seen them as something at the discretion of the author. As the reader, you have a plethora of tools to disengage from unwanted content on Mastodon—with even better filters coming in 4.0—and harassment is not one of them. People who are arriving now have as much right to be here and bring their own culture as the ones who came before them.
@Gargron New to the big M, so your comment is good to see. I see a discussion on the other site about CWs, which is overwrought about triggering. I understand the issue that person has, so am sympathetic.
I lost my 38-year-old son to suicide. (no sympathy comments needed, thanks) in 2014. I've been triggered twice since then. Once in a play and once in a movie. In the movie, I froze because if I hadn't, I would have broken down. I held it until the credits were finished. Left bruise marks on my wife's leg.
I recite this only to indicate I know about triggers. Also, there was no way for me to know I would be triggered because the trigger was not suicide but a father commenting on their living son.
It seems that CW usage is server specific. One federated post said politics requires a CW because that server was for a specific topic. They didn't want politics directly popping up in their feed. That's fine.
Just as each US state has different laws on some issues, like marijuana usage, each server can have different rules for CW. One state cannot enforce its rules in another state. A server can't enforce its culture on another.
Selecting the right server whose culture is to use CW to flag your trigger issue is the optimal solution, although that server may not exist.
I haven't grokked how the federated feed content is selected for presentation to an individual. I do understand that a server can block other servers, but that is a blunt tool for this situation. How many triggering messages cause a block? How many people have to generate triggers to cause a block? How many people need to be triggered to cause a block?
@rmerriam @Gargron There are tools provided to allow you to transfer your account to another instance, so that may help some people.