They are rarely useful (this is a hypothesis -- to be confirmed or refuted by ecosystem tests), they make our displayed types more complex/confusing, and their tendency to preserve intersections instead of simpler types can cause other issues (e.g. most recently #2200). Simplifying them out may improve performance due to more simple types instead of intersections (again a hypothesis to check on an actual PR.)

The easy approach here (good for a prototype PR to check the performance and ecosystem impact) would be to just strip them out in IntersectionBuilder::build.

If we decide we want to do this, the better approach might be to remove them entirely as Type variants, and replace with Type::remove_always_truthy and Type::remove_always_falsy transformers which can be used in type narrowing.