The idea behind Harbinger is that it can be trashed twice by cards that need installed card trashing to fuel their abilities, like Endless Hunger: the first time you turn it facedown, the second time it goes to your heap.
You also want to make sure you have a Harbinger out before you run with Endless Hunger on the board, if you're anticipating an X=0 Power Shutdown.
So, bear with me while I Jank God out for a minute. If you have Aesops pawnshop in play, plus a couple Reavers, and an Assimilator, you can play and trash a faceup Harbinger, bringing it back into play facedown. Then use two clicks to trigger assimilator, flipping it back faceup, and simply repeat the process over again ad infinitum. So in theory, once set up, you could be pulling 3 credits and 2-3 card draws for the price of two clicks anytime you want.
— ShaperLord777