The Kings may get some use out of Lecavalier as a 3rd or 4th line center, he's going to go for one last shot at the Cup so who knows, he may be motivated to perform better and has something to prove.
As for Schenn, he'll be playing behind Doughty, Muzzin, Martinez and McNabb and will serve as the right handed dman on the 3rd pairing that the team was looking for when they lost Matt Greene. He'll likely be paired with Christian Ehrhoff on the 3rd pairing, which is an upgrade over not having Matt Greene.
Given that they're both short term additions and depth moves, and they gave up no significant pieces from their roster and pipeline, it works. It also makes more sense with the amount of cap Philly is absorbing. Low risk, potentially high reward moves if the Kings go deep.
Considering how well they've performed with Weal not even contributing and Matt Greene out all season, the Kings just added some reinforcements without losing any roster player who was contributing. If it doesn't work out, it really doesn't hamper the Kings. It's like Lombardi did his old pal Hextall a favor and Hextall in a way did the Kings a favor by sending at the very least a serviceable, right handed defenseman that was needed.
Certainly cost them less getting Luke Schenn rather than going after a guy like Roman Polak who may cost a 2nd round pick and/or a prospect.