Added hint

app/src/main/res/layout/fragment_options_synchronize.xml

@@ -75,6 +75,19 @@
                 app:layout_constraintStart_toStartOf="parent"
                 app:layout_constraintTop_toBottomOf="@id/tvWhen" />
 
+            <TextView
+                android:id="@+id/tvPollHint"
+                android:layout_width="0dp"
+                android:layout_height="wrap_content"
+                android:layout_marginTop="6dp"
+                android:layout_marginEnd="48dp"
+                android:text="@string/title_advanced_poll_hint"
+                android:textAppearance="@style/TextAppearance.AppCompat.Small"
+                android:textStyle="italic"
+                app:layout_constraintEnd_toEndOf="parent"
+                app:layout_constraintStart_toStartOf="parent"
+                app:layout_constraintTop_toBottomOf="@id/spPollInterval" />
+
             <androidx.appcompat.widget.SwitchCompat
                 android:id="@+id/swSchedule"
                 android:layout_width="match_parent"
@@ -82,7 +95,7 @@
                 android:layout_marginTop="12dp"
                 android:text="@string/title_advanced_schedule"
                 app:layout_constraintStart_toStartOf="parent"
-                app:layout_constraintTop_toBottomOf="@id/spPollInterval"
+                app:layout_constraintTop_toBottomOf="@id/tvPollHint"
                 app:switchPadding="12dp" />
 
             <TextView

app/src/main/res/values/strings.xml

@@ -234,6 +234,7 @@
 
     <string name="title_advanced_enabled_hint">Globally disable or enable receiving of messages</string>
     <string name="title_advanced_manual_hint">If synchronization is disabled, it is still possible to synchronize manually by pulling down the message list. This will synchronize messages and execute operations for a limited time.</string>
+    <string name="title_advanced_poll_hint">Synchronizing periodically will compare local and remote messages each and every time, which is an expensive operation possibly resulting in extra battery usage, especially when there are a lot of messages to synchronize. Always synchronizing will avoid this by continuous listening for changes only.</string>
     <string name="title_advanced_schedule_hint">Tap on a time to set a time</string>
     <string name="title_advanced_metered_hint">Metered connections are generally mobile connections or paid Wi-Fi hotspots</string>
     <string name="title_advanced_metered_warning">Disabling this option will disable receiving and sending messages on mobile internet connections</string>