defineModel props default value

[dbzx10299]

In the docs for defineModel it states that

If you have a default value for defineModel prop and you don't provide any value for this prop from the parent component, it can cause a de-synchronization between parent and child components.

I don‘t understand why this is, isn‘t the point of a default value so that we don‘t have to provide a value. If we always provide a value from the parent then we don‘t need a default value anyways.