docs: add additional info on use_legacy_flow_control parameter

google/cloud/pubsub_v1/subscriber/_protocol/streaming_pull_manager.py

@@ -106,9 +106,11 @@ class StreamingPullManager(object):
             ``projects/{project}/subscriptions/{subscription}``.
         flow_control (~google.cloud.pubsub_v1.types.FlowControl): The flow
             control settings.
-        use_legacy_flow_control (bool): Disables enforcing flow control settings
-            at the Cloud PubSub server and uses the less accurate method of only
-            enforcing flow control at the client side.
+        use_legacy_flow_control (bool):
+            If set to ``True``, it disables enforcing flow control settings on the
+            Cloud PubSub server. Defaults to ``False``.
+            The less accurate method of enforcing flow control on the client side
+            is still enabled in both cases.
         scheduler (~google.cloud.pubsub_v1.scheduler.Scheduler): The scheduler
             to use to process messages. If not provided, a thread pool-based
             scheduler will be used.

google/cloud/pubsub_v1/subscriber/client.py

@@ -199,6 +199,11 @@ def callback(message):
                 *scheduler* to use when executing the callback. This controls
                 how callbacks are executed concurrently. This object must not be shared
                 across multiple SubscriberClients.
+            use_legacy_flow_control (bool):
+                If set to ``True``, it disables enforcing flow control settings on the
+                Cloud PubSub server. Defaults to ``False``.
+                The less accurate method of enforcing flow control on the client side
+                is still enabled in both cases.
 
         Returns:
             A :class:`~google.cloud.pubsub_v1.subscriber.futures.StreamingPullFuture`