[ceph-users] Deleterious effects OSD queue

Hi folks, Regarding OSD operation queues (shards), I found this in the documentation (https://docs.ceph.com/docs/master/rados/configuration/osd-config-ref/): "A lower number of shards will increase the impact of the mClock queues, but may have other deleterious effects". What are these deleterious effects? Why is it so bad to use just one queue for example? Is there any kind of bottleneck or costly procedures in these queues?