[NGW]

If it is a major plot point or twist or something? Then no, there doesn't need to be one. It's literally just being considerate. A lot of people jump into the fandom with no prior knowledge and they should expect to not have things spoiled for them. It takes literally no effort to tag something major like that.

And in a franchise that does have a wide variety of seasons, the majority of which are like their own standalone show, each with its own theme that may catch someone's interest at any random point in time, they should feel welcome and safe within the community to discuss or talk about things without worrying about something getting ruined for them.