Why extend the Vue.js constructor

Question

I’m studying Vue.js and I came across the method extend which in the documentation says it provides a subclass of the Vue’s base builder. I can understand that, but I couldn’t find a practical example of why I would do that. My doubts are:

• What are the differences between defining a local component and using the Vue.extend?
• In what situation would the use of Vue.extend be made public?