Why watcher is better than computed to perform asynchronous or expensive operations in response to changing data in vue.js?

Documentation of Vue.js says:

Using the watch option allows us to perform an asynchronous operation (accessing an API), limit how often we perform that operation, and set intermediary states until we get a final answer. None of that would be possible with a computed property.

While on the same page, we can see that computed property uses a function the same as watcher.

Reference: https://vuejs.org/v2/guide/computed.html#Computed-vs-Watched-Property

So my question is what is the technical reason supporting the above statement or limiting us from using computed properties instead of watchers?

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