It has been said many times since Arber Xhekaj officially made the team last year: he's not just a fighter. He's a defenseman who knows how to play hockey, as evidenced by some appearances on the second wave of the power play.
Martin St-Louis gave him chances to show what he's capable of, but overall, Xhekaj has been quite ordinary since the start of the season. Sending him to Laval clearly indicates that the organization doesn't intend to have a player just for dropping the gloves.
Certainly, on a third pair in Montreal, Xhekaj can't progress as much as if he plays a lot of minutes in a top-four role with the Rocket.
There you have it, the message is clear. The Canadiens are not satisfied with the play of the defenseman to the point where Xhekaj needs significant improvement in Laval. It's good news under the circumstances. The Canadiens are sending him down for development rather than putting his name on the trade market.