It's a good move by Montreal, not a ton of upside, but no downside.
Montreal needs to pick up a few players like this off of the scrap heap to fill roster spots when they trade a few guys away at the trade deadline.
It's better to take a relatively young player like White than older veterans.
Unlikely, as White has had his chances, but maybe they can salvage a serviceable 3rd / 4th line grinder out of White.
Again, there is no downside to this, and White is the type of player they should use to fill the upcoming empty roster spots.
White's problem (relative to becoming a good player, it's certainly not a life problem), is that thanks to Pierre Dorion's idiocy, he is set for life with like $16 million in career earnings. So he isn't as hungry to make himself into a useful player like guys with little career earnings would be.