In Vue, the `key` attribute is primarily used by Vue's virtual DOM algorithm to track reusable elements. When dealing with a set of elements that may dynamically change order or update items in a list, using `key` helps Vue accurately identify new elements versus reused ones. This can improve rendering performance and reduce potential rendering errors.

For example, if you have a list where each list item may be updated or reordered, you can use `key` as follows:

```html
<div id="app">
  <ul>
    <li v-for="item in items" :key="item.id">
      {{ item.text }}
    </li>
  </ul>
</div>
```

In this example, each `li` element is assigned a unique key based on `item.id`. When the `items` array changes, Vue uses `key` to determine which elements can be retained and which need to be recreated. This approach is particularly useful when sorting lists or replacing items within a list, as Vue can reuse DOM structures and component instances in place, preventing unnecessary element re-creation and component state loss.

How to Reuse Elements with the key Attribute in Vue?