After the investigation of HELP-47174 we realised the documentation for 4.4 and 5.0 mentioned that _secondaryThrottle=true will set automatically wc to majority in case is left empty for moveChunk.

However, this is actually true only starting from 6.0 and for previous versions wc is mandatory. 

This is important because in case of balancing, the moveChunk will inherit directly the configuration of the balancer, which might have an empty wc causing the entire balancing to block.

Correct the 4.4 and 5.0 doc to note that this setting is required and does not have a default value.

Current published docs:

v4.4
v5.0