There's a huge semantic difference: a type with zero allowed values can never be constructed.

This means that a function that returns an uninhabited type is statically known to not return -- since there's no way it could construct an uninhabited value for a return expression. It also means you can coerce a value of uninhabited type into any other type, because any code which recieves a value of an uninhabited type must be unreachable.

For instance, in Rust you can write the following:

    let weekday_name: &str = match weekday_number {
        1 => "Sunday",
        2 => "Monday",
        3 => "Tuesday",
        4 => "Wednesday",
        5 => "Thursday",
        6 => "Friday",
        7 => "Saturday",
        i => panic!("invalid weekday number: {i});
    };

Because panic! aborts the program and doesn't return, its return type is uninhabited. Thus, a panic! can be used in a context where a string is expected.

We were talking about `void`, not `!`. It's clear that "never" type has a special language support. Difference between `void` and `()` is much less subtle.

One vs zero is an incredibly fundamental difference.