That is in 4e option one of many many choices a Warlord might make and one could give to any Warlord build because flexible characters are a thing in 4e.Here a rough translation of an Epic Destiny from 4e to 5e.
The first lets the ally spend SOME HD when you use a second wind 5e level 15
The second one basically gives an ally your action surge. 16
One allows a bit of instant rest benefit shenanigans. 5e level 18
And the other allows allies to remain in the fight as long as you are Standing. 5e level 20
Even someone who just dabbled in Warlord earlier in the game.