Defense was an issue for the Bruins all season long so, in theory, going out and adding an experienced defenseman that was enjoying a strong season was a good idea.
By all accounts the move was a big flop, though. The Bruins generated almost 5% more of the shot attempts and 4% more of the scoring chances without Liles on the ice than with him. His individual numbers weren’t necessarily bad – he hovered ~49% in both categories – but you don’t want to be much better without a guy you just traded for than with him.
Factor in that the Bruins missed the playoffs and, again, they parted with a pair of draft picks (a 3rd and a 5th) in this deal and it makes matters much worse.
When you combine the Stempniak/Liles trades the Bruins parted ways with a 2nd, 3rd, 4th and 5th round pick for a couple rentals to play what were, in hindsight, meaningless games.