Why is ThemeOverlay needed?

Question

Android

I understand styles and themes. I just can't understand why themes with the ThemeOverlay prefix are needed?

There is such a definition on the web:
ThemeOverlay are special “lightweight” themes that allow you to override the attributes of the main theme for the View component.

But why should I use it if I can make my own theme with overriding the attribute I need? For example like this:

<resources xmlns:tools="http://schemas.android.com/tools">
    <!-- Base application theme. -->
    <style name="Theme.Styles" parent="Theme.MaterialComponents.DayNight.DarkActionBar">
        <!-- Primary brand color. -->
        <item name="colorPrimary">@color/purple_500</item>
        <item name="colorPrimaryVariant">@color/purple_700</item>
        <item name="colorOnPrimary">@color/white</item>
        <!-- Secondary brand color. -->
        <item name="colorSecondary">@color/teal_200</item>
        <item name="colorSecondaryVariant">@color/teal_700</item>
        <item name="colorOnSecondary">@color/black</item>
        <!-- Status bar color. -->
        <item name="android:statusBarColor" tools:targetApi="l">?attr/colorPrimaryVariant</item>
        <!-- Customize your theme here. -->
    </style>

    <!--Обычное переопределение темы-->
    <style name="Theme.Styles.CustomTheme">
        <item name="android:textColor">@color/red</item>
    </style>

</resources>

and to use this topic in the same way for one View as they say in the definition?

<TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:theme="@style/Theme.Styles.CustomTheme"
        android:text="TextView"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />