Pretty straightforward usage - the more of these you have, the more powerful the attack of this card and all your Outlands characters, Ethir Swordsman, Warrior of Lossarnach, Anfalas Herdsman, and notably, Forlong.
But lets look at some numbers to see how really strong this card is.
1 for one resource cost is already better than the 0.68 "per resource spent" average of the 55 Tactics ally cards released as of Cycle 9, AP 1 (Wrath and Ruin), and is clearly better than the other spheres average as well.
The second copy of this card on the table gives +2 to the party for a single resource cost, as both cards now total 4
Add the third copy of this card to the table, and you get a ridiculous +5 added for a single resource, as you go from 4 , to 9 (3 cards at 3 )
And that's not counting any other Outlands allies that would benefit....