By default VaValue provides reactive boolean value with false by default. Reactive variable passed to #default="v" slot bind and can be accessed or changed like ref. Bellow is example of toggle value on description click v.value = !v.value.
Great example where VaValue can be useful is v-for or v-slot. In example below we render form data with v-for and for each item VaValue creates state, which we use to change if it is in edit mode or not.