When you include notes about content, and your policies, that helps people make more informed and mindful decisions about their lives. When you include tools -- you may ask for an alternate assignment, here is the quiet room, this is a handout of coping skills because this class handles historic atrocities, if you are having lots of trouble please visit in my office so we can discuss it, etc. -- that teaches people how to handle challenges in effective ways that build resilience. There are rocks, but you can climb over them. Here is a rope.
When you do not include notes, you deny people the chance to select the classes that are the best fit for them and to cope with materials presented in progress. There are rocks and people are dropped on their heads. If you sustain a concussion it is because you are a pussy, not because the rocks are sharp.
When you include notes but not tools, and allow people to dodge material without compensating in any way, that is coddling. The rocks are taken out of the way. Now nobody can learn how to climb rocks in a relatively safe environment.
The complaints about trigger warnings basically say: "It is okay to hurt people. It is not okay if you want people NOT to hurt you. Just get used to being hurt, you pussy." Because really? If you have triggers, there is no getting away from them. The world whacks them all the time. Especially if they are about sex or violence or both. And pressuring people to remain silent about being hurt just gets more people hurt, which is also not okay.
When you put content notes or trigger warnings on a class, story, or other material it says: "I am choosing to deal with controversial topics. I want to understand what happens in the world and hopefully that will help make it a better place. I want to make it as accessible as possible so that more people can deal with these topics in a safe way." You don't go into shop class and NOT have safety goggles, I hope. If you're talking about things like rape or mass murder, and especially about some crackpot thinking those are jolly good ideas, then folks need to know that appropriate safety measures are in place.
Seriously, look around: If there are women, about a quarter of them have experienced sexual violence personally and the rest have at least fended off smarmy approaches. Probably at least one or two of the men are survivors too. If there are Jews, they will be sensitive about the Holocaust and probably Israeli politics. If there are black people, they will be sensitive about slavery and racism. If there are poor people, they will probably be touchy about some money issues. And if the group is a monoculture, that's likely to cause problems on its own and is not an ideal learning environment. Explaining the parameters for handling challenges is just part of running a smooth class or other activity. It is not fun for anybody if somebody has a panic attack because they got blindsided. It is not effective if people blank out because the material is ghastly and no coping methods are available.
Of course, not everyone is equally good at listing triggers, and it does take time. So if that's expected at college, you have to allow the extra time and make sure there's a backup person for teachers who aren't good at it. (Inaccurate warnings are worse than useless.) If you're doing it as a writer, you can just ask your audience to tell you if they think more warnings are advisable.