Why should I use an CATransaction in an animation?

Question

I've found this code snippet:

[self setValue:direction forKey:@"currentDirection"];

CAKeyframeAnimation * animation = [CAKeyframeAnimation animationWithKeyPath:@"position"];
animation.path = path;
animation.duration = grids * gridWidth / [self speed];
animation.fillMode = kCAFillModeForwards;
animation.removedOnCompletion = NO;
animation.delegate = self;
animation.calculationMode = kCAAnimationLinear;
[self addAnimation:animation forKey:@"movement"];
self.position = destination;

[CATransaction begin];
[CATransaction setValue:[NSNumber numberWithFloat:_turn_duration]
                                          forKey:kCATransactionAnimationDuration];
eyes.position = eyeDestination;
pupils.position = pupilDestination;
[CATransaction commit];

CGPathRelease(path);

What's the point of using the CATransaction here?

Answer 1

To set the duration of the two implicit animations within the transaction to a value different from the duration of the keyframe animation above. The animations inside the transaction will run over _turn_duration seconds, while the keyframe animation will run over grids * gridWidth / [self speed] seconds.