Use part to depletion?

[MacAaroni]

Curious what's the reasoning behind when a part says to use till depletion then calls to use another part? In this case it's Moog swaybar links for my 06 Sierra. There are two versions, but it says to use one version first then a different version after depletion. Can i not use the second version right from the get go? Will it cause problems? What is this madness? 

[Mike GMC]

At least for me, that description does not provide enough info on the specific situation to answer accurately.  But my guess is, " depletion" means stock.  Meaning the stores should sell out the old part number first.  I have no idea if the new part is better, or just slightly different.