Working on a real case scenario in a five node Percona XtraDB Cluster (PXC), we were forced to use wsrep_sync_wait = 1, because the app does reads-after-write and we send reads to all the nodes. We had the idea to leave some nodes in DESYNC mode to reduce the flow control messages during peak load [&]

https://www.percona.com/blog/pxc-scheduler-handler-the-missing-piece-for-galera-percona-xtradb-cluster-puzzle/