There is no problem here with the critical region. The problem would be removing the critical region because "there's just one thread".

This is incorrect code

      a = foo();
      b = io(a).await;
      c = bar(b);

Without the lock, `a` can mutate before `b` is done executing which can mess with whether or not `c` is correct. The problem is if you have 2 independent variables that need to be updated in tandem.

Where this might show up. Imagine you have 2 elements on the screen, a span which indicates the contents and a div with the contents.

If your code looks like this

    mySpan.innerText = "Loading ${foo}";
    myDiv.innerText = load(foo).await;
    mySpan.innerText = "";

You now have incorrect code if 2 concurrent loads happen. It could be the original foo, it could be a second foo. There's no way to correctly determine what the content of `myDiv` is from an end user perspective as it depends entirely on what finished last and when. You don't even know if loading is still happening.