Why should I use a Linearlayout within another Linearlayout?

Question

I don’t understand this example:

   <ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >
    <LinearLayout


    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical" >
    <LinearLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="#015488"
    android:orientation="vertical" >
    <TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="center"
    android:text="@string/novo_gasto"
    android:textAppearance=
        "?android:attr/textAppearanceLarge"
     android:textStyle="bold" />
         <TextView
        android:id="@+id/destino"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:textAppearance=
"   ?android:attr/textAppearanceLarge"
        android:textStyle="bold" />
        </LinearLayout>
        </LinearLayout>
        </ScrollView>