Multiple pool options in Antminer S9 Settings I have purchased and got running Antminer S9. While setting it up I notices that I can specify three pool connections 



I was unable to find the purpose for this.

Are those backup options just in case one or two pool connections are down or should I could actually mine for three pools at the same time?
The AntMiner S9 manual is available at https://shop.bitmain.com/files/download/AntMiner%20S9%20Installation%20Guide.pdf

The manual says:


  The AntMiner S9 can be set up with three mining pools, with decreasing
  priority from the first pool (pool 1) to the third pool (pool 3).
  
  The pools with low priority will only be used if all higher priority
  pools are offline.


On older S-series models there used to be a "Pool Balance" setting on the pool screen, below the "pool 1", "pool 2", "pool 3" in your screenshot. From the manual for the old S3:


  AntMiner can set up three mine pools, the priority decreases from
  first pool (pool 1) to third pool (pool 3). There are three Pool
  Balance option:
  
  Failover: Automatic backup when Miner faults;
  ‘Failover’ is by default. The low priority pool will start to work,
  only when the high priority pool encounter fault.
  
  Balance: Change
  multipool strategy from failover to even share balance.
  
  Load Balance:
  Change multipool strategy from failover to quota based balance.


I do not know why this feature was removed in later models.