If a user submits a configuration change to drop a shard, Atlas will sift through the cluster metrics and advise any necessary changes needed in order to complete the change without any errors/delays. For example, it will share the correct number of IOPS/cluster tier that needs to be used since the workload to drain a shard will increase; as well as other precautionary measures that should happen prior to dropping the shard (i.e. balancer needs to be turned on, etc).