Further explanation about why side-effects should be limited to useEffect

There are multiple recommendations about when side-effects are okay and when they are not okay; it is difficult to memorize them all, so it would be helpful if some further explanation is added explaining exactly why useEffect should be exclusively used for side effects e.g.
https://github.com/reactjs/reactjs.org/blob/master/content/docs/hooks-effect.md#example-using-classes-example-using-classes

For traditional life-cycle hooks, the reasoning is that some of them might be called multiple times before the render is committed; is the same applicable to hooks?

Thanks!

p.s. This comment seems relevant:
https://github.com/reactjs/reactjs.org/issues/302#issuecomment-345445888

從連結的 Hooks Effect 文件章節開始，將其中對類別生命週期方法的討論與目前對副作用和 useEffect 的指引進行比較。更新文件，清楚說明為什麼副作用應放在 useEffect 中，並說明相同的重複呼叫疑慮是否也適用於 hooks；當不必記住各自獨立的規則就能理解這項建議時，即表示完成。