keep guide stuff to guides

Author: gaearon

beta/src/content/apis/react/useEffect.md

@@ -20,11 +20,9 @@ useEffect(setup, dependencies)
 
 ### Connecting to an external system {/*connecting-to-an-external-system*/}
 
-There are two kinds of logic in your React components. Code that only calculates something is called *pure.* For example, transforming some data into JSX is a [pure calculation.](/learn/keeping-components-pure) The rest of your logic *does* something: for example, it may send a network request in response to a button click. That kind of logic is called a ["side effect".](https://en.wikipedia.org/wiki/Side_effect_(computer_science))
+Sometimes, your component might need to stay connected to the network, some browser API, or a third-party library, while it is displayed on the page. Such systems aren't controlled by React, so they are called *external.*
 
-Most of your side effects will be inside [event handlers](/learn/responding-to-events) like `onClick`. However, when a component needs to run some code *in response to being displayed* rather than to any particular interaction, you need to [declare an Effect.](/learn/synchronizing-with-effects#how-to-write-an-effect) For example, your component might need to stay connected to the network, some browser API, or a third-party library, while it is displayed on the page. These systems aren't controlled by React, so they are called *external.*
-
-To connect your component to some external system, call `useEffect` at the top level of your component:
+To [connect your component to some external system,](/learn/synchronizing-with-effects) call `useEffect` at the top level of your component:
 
 ```js [[1, 8, "const connection = createConnection(serverUrl, roomId);"], [1, 9, "connection.connect();"], [2, 11, "connection.disconnect();"], [3, 13, "[serverUrl, roomId]"]]
 import { useEffect } from 'react';