Merge pull request #6324 from EnterpriseDB/DOCS-733-subscribery-only-…

…clarity

DOCS-733 - Added clarity to subscriber-only node purpose.

product_docs/docs/pgd/5/node_management/subscriber_only.mdx

@@ -2,6 +2,9 @@
 title: Subscriber-only nodes and groups
 ---
 
+Subscriber-only nodes provide a means to scale up the handling of read-only
+requests in PGD. 
+
 ## Subscriber-only nodes
 
 As the name suggests, a subscriber-only node subscribes only to replication
@@ -25,7 +28,10 @@ this topology, a small number of fully active nodes are replicating changes in
 all directions. A large number of subscriber-only nodes receive only changes
 but never send any changes to any other node in the cluster. This topology
 avoids connection explosion due to a large number of nodes yet provides an
-extremely large number of `leaf` nodes that you can use to consume the data.
+extremely large number of `leaf` nodes that you can use to service a large 
+number read-only requests without adding load to the replicating cluster.
+
+
 ## Subscriber-only groups
 
 To make use of subscriber-only nodes, first create a PGD group of type