There isn't a massive difference between type instability vs programming against interfaces in OOP languages or using a Box<dyn T> in Rust, both add an extra indirection which has a performance impact, but depending on the situation it could be a positive or negative impact.
it has a huge impact on static analysis to know that the type is a Box<dyn T> in rust, and you can't (without something else) downcast Box<dyn T> to a specific U.
i don't care about the performance as much the correctness :)
