AMIS30543 | DataSheet Understanding CIRCULAR TRANSLATOR TABLE
1. It describes the current going through the two coils of the stepper motor at each step.
2. I'm not quite sure, as I I would think the last two diagrams should actually be squares. But for example in the first image you can see that the current in the X coil will steadily increase, while the current in the Y coil will steadily decrease. This will make the stepper rotate more slowly.
In the second image you can see that only the Y coil driver at 100% in step 0. In step 1 both coils are at 100%. In step 2 coil Y is turned off. I think this is profile produces more torque, but is less smooth.
3. No. I you are, for example using full step mode, and the motor is in step 0. If you give it 3 steps forward  (while the motor is disabled) it would drive the coils (once you re-enable to motors) as describe in the lookup table for step 3. Which in practice would mean the motor would rotate backwards one step (instead of 3 steps forward).
In other cases it could result in undefined behavior. Going from step 0 to step 2 could mean if would rotate clockwise, anticlockwise, or even not rotate at all.
Though in practice I don't think this you would even be in issue, and disabling the motor, but still sending it step pulses is kind of silly.