It is the opposite, you are telling the compiler that you want the value to be undefined.
And there aren’t enough safety checks yet so that all ways to use such an undefined value would be caught reliably. So for now you have to be careful and it is better to only use undefined, when you are making sure that you are setting it to a valid value before you actually use it.
In cases where some field sometimes needs to be set to undefined, it is better to avoid using a field default value for that and instead pass undefined for that field value explicitly during initialization/setup.