"Allow multiple values" vs "Allow multiple filter values to work together" In Views, when adding an Argument for a vocabulary term id, I'm presented with the following 2 options:

Allow multiple values
If selected, users can enter multiple values in the form of 1+2+3 (for OR) or 1,2,3 (for AND).

Allow multiple filter values to work together
If selected, multiple instances of this filter can work together, as though multiple values were supplied to the same filter. This setting is not compatible with the "Reduce duplicates" setting.

The first option is perfectly clear to me. The second, however, I'm struggling with. What exactly does it do, and how does this differ from the "Allow multiple values" option?

Can the two of these options be used together? If so, what would be the expected outcome?

Thanks!
Allow multiple filter values to work together is used when you want to pass multiple arguments to and match against one field. 
In other words allows for 'many to one' joins

In a sense it is similar to 1, 2, 3, however if you need to pass multiple sets like 123+345 and 889+678 there need to be 2 separate joins to the same table. 

(assuming sometable has multiple results for your desired value like:

|nid|yourvalue|

|1  |123      |

|1  |345      |

|2  |678      |

|3  |222      |

|1  |789      |

|1  |823      |

|1  |845      |

|2  |678      |

|3  |222      |

|1  |889      |

select node.title from node node 
join sometable sometable_1 on sometable.yourvalue in (123,345)
join sometable sometable_2 on sometable.yourvalue in (889,678)

Therefore 'Allow multiple filter values to work together' is the only way to get view to return nid 1

this is useful when you need to pass arguments that come from different sources (i.e. 1 could be taxonomy terms from 2 different vocabs).

I used this only when dealing with entityreference field that references terms from different vocabularies