The Resharding Improvements Atlas log request shows that the server will be emitting a log line for every resharding operation with the start and end date and times. Currently the only collection level detail captured in the logs is the original and new shard key. 

For a better understanding of feature performance the following  metrics should be added:

• Number of Documents
• Average Document Size
• Collection Size
• Number of Indexes
• Number of Source Shards
• Number of Destination Shards
• Operation Duration (done in SERVER-80957)