Garland is a terrific scorer and shot creator for a point guard, ranking in the 86th percentile in points per shot attempt and the 80th percentile in assists per usage rate. As a result the Cavs score 6.6 points more per 100 possessions when Garland is on the floor.
His weakness is turnovers, where he ranks in the 26th percentile among point guards. He makes a lot of brilliant passes but throws too many away, especially when he takes it into the paint and tries to kick it out to a corner. If he could get the turnover rate down about 35% or so he would be even better offensively. That's his next challenge, IMO, and the last big hurdle to overcome before he becomes an elite point guard.
Ricky Rubio's turnover rate was almost as high as Garland (14.6% against 15.9%). So far Brandon Goodwin is at 8.4%, putting him in the 90th percentile among point guards. That's because he's not as willing to throw risky passes as the two more experienced and confident point guards. Speaking of experienced and confident, Rajon Rondo is at 18.4%, which is the highest turnover rate on the team in limited action. But his assist per usage rate is the highest, indicating he's more inclined to throw high risk/high reward passes than anybody.
As a team the Cavs rank 28th in the NBA in turnovers per possession. But Golden State is 29th so it's a mixed bag. A high turnover rate probably indicates you're throwing aggressive, high risk passes that either result in high percentage shots or turnovers. The Warriors are only 14th, barely above average, in offensive efficiency, so I think they could stand to be a little less aggressive in their passing.
The other two Cavs' players who rank very low in terms of turnovers are Allen and Okoro. Allen tends to fumble a lot of passes and he gets stripped in the low post when he doesn't protect the ball well enough while setting up his shot. He needs to work on looking the pass into his hands and securing the ball before looking to shoot and also avoiding getting stripped on the way up. Okoro needs to learn how to dribble with his left hand without losing the ball.