[4.1.x] Fixed #30801 -- Improved guidance for making good use of signals.

Backport of 71e9694856 from main

docs/ref/signals.txt

@@ -22,6 +22,14 @@ Model signals
 The :mod:`django.db.models.signals` module defines a set of signals sent by the
 model system.
 
+.. warning::
+
+    Signals can make your code harder to maintain. Consider implementing a
+    helper method on a :ref:`custom manager <custom-managers>`, to
+    both update your models and perform additional logic, or else
+    :ref:`overriding model methods <overriding-model-methods>` before using
+    model signals.
+
 .. warning::
 
     Many of these signals are sent by various model methods like
@@ -550,6 +558,12 @@ Request/response signals
 
 Signals sent by the core framework when processing a request.
 
+.. warning::
+
+    Signals can make your code harder to maintain. Consider :doc:`using a
+    middleware </topics/http/middleware>` before using request/response
+    signals.
+
 ``request_started``
 -------------------