What is MU-MIMO Grouping QoS Level?

What is this setting for and what should it be set to? There's no mention of it that I can find in the 16.0.1 user guide.

In prior software, only the low priority channel data was able to be grouped into MU-MIMO groupings... That is, any high priority traffic was transmitted first (in SU-MIMO mode), then the low priority was grouped and transmitted in MU-MIMO where possible to optimize throughput.

Now, you can choose to have any priority traffic be considered for MU-MIMO grouping (depending on the selection in this dropdown).  Therefore, it won't necessarily be transmitted before other traffic, but could be simultaneous with other SM transmissions (i.e. in MU-MIMO mode).  Depending on the complexity of your QoS priorities within the sector, grouping multiple priorities may work well for you or not.

By example, if you have customers doing VoIP in the sector (and they are using the highest priority), you may want to exclude them from grouping such that they are absolutely prioritized, resulting in seamless VoIP quality regardless of AP load. But customers doing other things (even paying more for higher QoS) may be able to be grouped, and won't be impacted by participating in MU-MIMO grouping. The result would be optimizing the capacity of the sector, while maintaining QoS.