Having established what this part is (see post https://www.x-trail-uk.co.uk/viewtopic. ... 85&t=76317 )
I now think I understand it's function.
(1) The valve closes to create back pressure to allow low pressure EGR to aid reduction in NOx
(2) When valve opens after low pressure EGR it creates a strong pressure wave to expel gasses through exhaust system creating a scavenging effect
to help move carbon particle through exhaust system.
(3) Because of the back pressure in exhaust it also helps to increase temperature within exhaust system to increase temperature within catalytic converter and DPF.
(4) Any fault/failure with the Exhaust electric throttle control actuator could have a detrimental effect on other parts of the exhaust/EGR systems.

Can anyone confirm if my basic understanding is correct.