Arenas last played for the Orlando Magic last season averaging 8 points-per-game and 3 assists-per-game. He was amnestied before this season by the Magic and has yet to play this year.
The Grizzlies have long tried to improve their depth behind starting point guard Mike Conley after Josh Selby and Jeremy Pargo proved to be insufficient to back him up this season. Arenas will fill that role nicely and give Conley time to rest during the game.
Arenas boasts career averages of 21 PPG and 5.4 APG, and if he can come anywhere near that production, this will turn out to be a huge steal for the Grizzlies. He still has the ability to go off for 20+ points on any given night, which would give them a huge lift on the offensive end.
Arenas will provide a huge scoring boost for the Grizzlies' bench and team with guard OJ Mayo. They would form a dynamic backcourt duo that can take over games at any given time. He instantly makes the Grizzlies one of the deeper teams in the NBA and will take pressure off of the starting lineup to score.
He also provides playoff experience and veteran leadership to a young squad that is talented but lacks experience. While he has had some off-the-court issues in the past, he showed signs of maturing last season as he served as a mentor to John Wall before being traded to the Magic mid-season.
Arenas is reportedly in good shape and this will help him make contributions immediately, instead of having to get into basketball shape. If he can still play at a high level, he makes the Grizzlies a much more dangerous team as they prepare for a playoff run.
His scoring will be extremely useful when the Grizzlies' starters have an off-day, as he can still carry an offense on occasion and he has Mayo to help him on that end, as well.
Overall, this is a no-lose situation for the Grizzlies. If he plays anywhere near the level he did during his prime, this will turn out to be a huge steal for the Grizzlies and would give them a sufficient backup for Conley, as well as another offensive threat. If he doesn't play well, then they didn't lose anything, as he is only on an one-year deal.