docs: remove importance of shallow mount

Author: afontcu

docs/guides/common-tips.md

@@ -27,6 +27,8 @@ const wrapper = shallowMount(Component)
 
 Like [mount](../api/#mount), it creates a [Wrapper](../api/wrapper) that contains the mounted and rendered Vue component, but with stubbed child components.
 
+Notice that using `shallowMount` will make the component under testing different from the component you run in your application – some of its parts won't be rendered! This is why it is not the suggested way of testing components unless you face performance issues or need to simplify test arrangements.
+
 ### Lifecycle Hooks
 
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