There's a good article on the Examiner website about Rassie Erasmus and Jacques Nienaber's coaching impact while at Munster from the perspective of Duncan Williams, Duncan Casey and Ronan O'Mahony. It's well worth reading. One thing really stood out for me:

Erasmus and Nienaber made an immediate positive impact at both Munster and South Africa. As an assistant coach, Stuart Lancaster made an immediate positive impact on Leinster's playing style having only arrived two games into his debut season.

As a head coach, Johann van Graan hasn't really laid down a marker yet in this his third season. As an assistant coach, Stephen Larkham hasn't made an immediate impact on the style of play. Is he being hampered by the head coach wishing to impose another more attritional style? I don't buy the argument that Munster regressed due to international players not getting to work with the new backs coach while the World Cup was on.

JP Ferreira on the other hand has done a fantastic job as defence coach.