As the title says.
For example, if I have this:
<queries>
<intent>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.HOME"/>
</intent>
...
<intent>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.HOME"/>
</intent>
The second one isn't needed.
You can also add this for merged manifest, but it's a bit more dangerous... If you add it there, please mention where it already exists, and point to it.