Why should I use MaxScale readwritesplit router over a three node Galera cluster?

In the following official MariaDB blog Getting Started with MariaDB Galera and MariaDB MaxScale the author configures a MaxScale host over a three node Galera cluster, and uses the Galer monitor (OK) and the readwritesplit router, It is not clear for me, if I spread all transactions equally (or optionally weighted) on all nodes, including writes, why would I bother to split read and writes? What would be the benefit of this added complexity? In reagards of performance what would be the preferred MaxScale router?