docs: mention LWT optimisation in default policy

Author: wprzytula

docs/source/load-balancing/default-policy.md

@@ -166,5 +166,11 @@ And only if latency awareness is enabled:
 
 If no preferred datacenter is specified, all nodes are treated as local ones.
 
-Replicas in the same priority groups are shuffled. Non-replicas are randomly
+Replicas in the same priority groups are shuffled[^*]. Non-replicas are randomly
 rotated (similarly to a round robin with a random index).
+
+[^*]: There is an optimisation implemented for LWT requests[^**] that routes them
+to the replicas in the ring order (as it prevents contention due to Paxos conflicts),
+so replicas in that case are not shuffled in groups at all.
+
+[^**]: In order for the optimisation to be applied, LWT statements must be prepared before.