DOCS-983: edits

Author: Sam Kleinman

source/includes/warning-splitting-chunks.rst

@@ -1,9 +1,11 @@
 .. warning::
 
-   Be careful when splitting chunks. When you shard a collection that
-   has existing data, MongoDB automatically creates chunks to evenly
-   spread the collection. Performing additional splits requires
-   knowledge of the resulting chunk sizes by numbers of documents and by
-   size. You do not want splits that cause some chunks to be much larger
-   than others. This leads to balancing based on count of chunks, not on
-   their size, which may cause extreme load/data-distribution problems.
+   Be careful when splitting data in a sharded collection to create
+   new chunks. When you shard a collection that has existing data,
+   MongoDB automatically creates chunks to evenly distribute the
+   collection. To effectively split data in a sharded you must
+   consider the number of documents in a chunk and the average
+   document size to create a uniform chunk size. When chunks have
+   irregular sizes, shards may have an equal number of chunks but have
+   very different data sizes. Avoid creating splits that lead to a
+   collection with differently sized chunks.

source/tutorial/manage-chunks-in-sharded-cluster.txt

@@ -103,13 +103,12 @@ chunk splits.
 Create Chunks (Pre-Splitting)
 -----------------------------
 
-Pre-splitting lets you preemptively split chunks in an empty collection
-and is used *only* in certain situations.
-In most situations a :term:`sharded cluster` will create and distribute
-chunks automatically without user intervention. However, in a limited
-number of use profiles, MongoDB cannot create enough chunks or
-distribute data fast enough to support required throughput.
-For example, if:
+Pre-splitting the chunk ranges in an empty sharded collection, allows
+clients to insert data into an already-partitioned collection. In most
+situations a :term:`sharded cluster` will create and distribute chunks
+automatically without user intervention. However, in a limited number
+of use profiles, MongoDB cannot create enough chunks or distribute
+data fast enough to support required throughput.  For example, if:
 
 - you must partition an existing data collection that resides on a
   single shard.
@@ -384,4 +383,3 @@ bulk insert operations:
   and see :ref:`Shard Key Internals <sharding-internals-shard-keys>` (in
   particular, :ref:`sharding-internals-operations-and-reliability` and
   :ref:`sharding-internals-choose-shard-key`).
-