I have a cousin who once went to a movie she expected to be lighthearted and family friendly, and she was blindsided by a heart-rending situation presented by the movie that was similar to one she had just experienced - no one had warned her to be ready for it, or else she might have chosen a different movie. I would hate to have the same thing happen to one of my readers. So, I have tried to be aware of potentially sensitive topics and to put an alert on my webpages to help readers choose which stories would be best for them - and which would not.
While I do not shy away from difficult and/or traumatic topics, I also do not intentionally try to horrify my readers. I do not write explicit sexual scenes of any kind. I may have characters who use curse words, but those words are not explicitly stated (unless they are euphemisms with no objectionable meaning in our culture - such as "by the cetus!"). There is often some form of violence in my stories, but I limit the gore as much as I can. If I can soften a situation by eliminating descriptions, I often will.
If a potentially sensitive topic is followed by "(mentioned)", that usually means the topic took place before the events of the book started and is therefore only present in conversation. For example, one of my characters had a parent commit suicide when he was a child. As a grown man in the story, he is still dealing with the grief from it and learning how to cope and forgive and heal. It is a vital part of the story, but because the event happened in the past and is only talked about, not described in real time, the warning on the webpage is "Suicide (mentioned)".
If a topic is followed by "(not explicit)", that means the event happens in real time during the story but is not described in detail. For example, if a characters falls into the hands of the enemy and is tortured for information but the story skips ahead to when the character is healing from his injuries, the warning reads, "Torture (not explicit)".
I hope that helps clear things up. If I miss a potentially sensitive topic, feel free to inform me of it by commenting on my blog. Thanks!