CWs are more art than science. In the current Mastodon culture, some topics like politics, NSFW, violence, etc. are almost required to have CWs.

For other stuff it's up to your discretion: alcohol, food, selfies, eye contact, etc. Mental health topics often use "mh" with a +, -, or ~ for positive, negative, or neutral.

A good CW can set up the punchline to a joke! A bad CW can spoil a joke. It's tricky.

Ultimately it's about empathy for your readers. You'll get the hang of it. 🤗