DOCS-305 additional corrections after technical review

Author: Sam Kleinman

source/release-notes/2.2.txt

@@ -154,13 +154,19 @@ reporting for concurrency and use, see the :ref:`locks` and
 Improved Data Center Awareness with Tag Aware Sharding
 ``````````````````````````````````````````````````````
 
-In 2.2, MongoDB adds additional support for geographically distributed
-database systems. This "tag aware" sharding combines with work done
-with :ref:`read preferences <replica-set-read-preference>` and
-:ref:`tag sets <replica-set-configuration-tag-sets>` to make it
-possible to ensure that data in a geographically distributed sharded
-cluster is always closest to the application servers that will use
-that data the most.
+
+In 2.2, MongoDB adds additional support for geographic distribution or
+other custom partitioning in shard clusters.  By using this "tag
+aware" sharding, you can automatically ensure that data in a
+sharded database system is always closest to the application servers
+that use that data most frequently.
+
+Shard tagging controls data location, and is complementary but
+separate from replica set tagging which controls data access.  For
+example, shard tagging can pin all "USA" data to one or more logical
+shards, while replica set tagging can control which :program:`mongod`
+instances (e.g. "``production``" or "``reporting``") the application
+uses to service requests.
 
 See the documentation of the following helpers in the :program:`mongo`
 shell that support tagged sharding configuration: