Reusing SRAM 10 Speed PowerLock?
It's not so much that reusing the link increases the chance that the pins or plates that the Powerlock is made up of will fail, but rather that it increases the chance that the link will come apart the same way it was put together. Each time you remove that link it wears down the "ridge" that snaps the pins in place on their opposing plates. This increases the chance that the link can undo itself in unusual circumstances. It may also slightly increase the chance of the link failing in the case of shifting under heavy load, which should be avoided anyway.

SRAMs 9 speed quick links were notorious for coming apart on the trail as they are reusable- some of this had to do with improper removal which damaged the relief that held the pins in place. It's probably easier for the company to just say "don't do it" than to say "do it this way" and folks don't adhere to the manufacturer's recommendations, leading to failures.

TL;DR version- if you only remove the link on occasion, its good for the life of the chain. Don't reuse an old quick link on a new chain.