Because sometimes just one choice isn't enough, you need to allow users to select multiple options. That's when you include a multiselect dropdown on your form.
In some online forms, you might need users to enter a phone number. Wouldn't it be great if your Angular application formatted that phone number on the fly?
When basic form field validation isn't good enough, you might need to check some input against the database. And to handle that task, you'll need to implement an asynchronous validation solution.