When its required
It is required when you have the list of items and you have to select multiple items from the list.
Let me explain with an example –
You are creating a department information form where you also have the list of users, In that case for assigning users you need to check them one by one.
In some cases, you need to assign all users to a department for that you either do it by checking one by one which is a time-consuming process when you have lots of users or create a separate checkbox for this. On a single click, you can either checked them all or uncheck it.