It can be said that when teams are trying to fill out their roster or realize that they have injuries on their roster and have to try to find replacements, that some of the players or replacements are not going to turn out great.
Well in terms of one of the two players that the Penguins wish they never had on their roster, was not good his first time in Pittsburgh and got a second chance as an injury replacement, and was not good the second time either.
As for the other player, i am pretty sure he has gotten two separate stints in Pittsburgh and also was not very good in either stint. These are definitely players that general manager Kyle Dubas wishes he never had on his roster.
Defenseman PO Joseph
Joseph received a lot of backlash from Penguins fans this past season because he received a second chance being acquired early in the season from the St. Louis Blues in a trade for pretty much no return and was not good in his second try with the big club.
Joseph is not very big and not very strong for playing as a defenseman and he constantly got hit and knocked down and a lot of the speedy forwards on other teams would go right around him.
The move to reacquire him for literally nothing seemed fine at the time, but Dubas having to watch Joseph's second stint on the team, was not fun and very regrettable.
Forward Matt Nieto
This one is pretty easy to evaluate. Nieto was never anything more than a 4th liner who thought he was good on the penalty kill, but was actually terrible at that too.
He was not a good skater and for whatever reason when Mike Sullivan was still around, Sullivan loved Nieto and loved playing him in big moments trying to protect leads late in the game.
That strategy usually never worked out as his line would allow a lot of offensive zone time and allow tying goals all the time. This was another player that Dubas had a tough time watching and another move he regretted making even if he did not make a ton of money at the NHL level.