Why do the Sabres do that?

Martinez can play both sides, and logs heavy minutes with both Pietro and Theodore so he would likely be a good complement for Dahlin or Power. Zero cost to acquire for a solid top 4 dman is a pretty good value. He's also a monster shot blocker.

yeah honestly if the NTC isnt an obstacle this is a sneaky good 1 year move. Especially if the price is this low

Yes, definitely, on Martinez. At the very least, he would be terrific on Buffalo's third pair to win his minutes, contribute to PK, serve as top-4 injury insurance.

I'd still want to acquire a younger top-4 D for regular duty.