I have seen that "Stopping balancer to prevent all meta-data change of config server" from a few mongodb documents.

For example,
http://docs.mongodb.org/master/release-notes/2.4-upgrade/#
Turn off the balancer in the sharded cluster and stop all meta-data operations. If you are in the middle of an upgrade process (Upgrade a Sharded Cluster from MongoDB 2.2 to MongoDB 2.4), you have already disabled the balancer.

So I have thought, If I stop balancer all config server's access(query/insert/update/delete) is stopped automatically. Config server's data is never changed during balancer stop.

But, I found that auto chunk split is active even balancer is stopped recently.
I think chunk split is also important meta data change like chunk migration.

Here's question.
Why MongoDB has only balancer stop not auto split. ?
Meta data change of auto splitting chunk is not harm meta-data upgrade(Upgrading mongodb) ?
Does chunk migration has any special things rather than chunk split ?