I know people on here are going to make fun of whatever team signs Bogosian, but I feel like those people are going to be ignoring the real positive of signing Bogosian: free depth is better than trading assets for depth. I don't know much about the other team's defense situation, but at least with Pittsburgh, he's not playing when the team is healthy. It's better to sign a guy for league minimum to have as an extra D over trading a 3rd or 4th for an equivalent D, because that's what Bogosian caliber rental D tend to cost at the deadline. Is the asset saved substantial? No, but it's an asset you can use elsewhere to improve your roster.
It's the same argument for signing Kovalchuk when he had his contract terminated. If Kovalchuk was a rental on LA, he would have cost something to acquire. Even with his flaws, signing him would save you assets that you'd use down the line to acquire another depth forward. That's exactly what the Penguins are going to do, they're going to trade like a 4th for Sheary when they could have had Kovalchuk for free.