DRV2605L: Software addressing the DRV2605 waveforms

Both Adafruit and Sparkfun provide software support for the DRV2605 and select waveforms to play like this (Arduino target host):

void loop() {
  Serial.print("Effect #"); Serial.println(effect);

  // set the effect to play
  drv.setWaveform(0, effect);  // play effect
  drv.setWaveform(1, 0);       // end waveform

  // play the effect!
  drv.go();

  // wait a bit
  delay(500);

  effect++;
  if (effect > 117) effect = 1;
}

I'd like to understand the motive and effect accomplished with the drv.setWaveform(1,0) command here (saying "end waveform").

Some questions:

1. Say you write to start one effect waveform.  Does it start right away or first verify there is not already a waveform being played?  Does the "end waveform" write do anything to the status of the previous write - is the previous waveform guaranteed to play full length?

2. What happens if you write one effect waveform and then a 2nd right after, without the "end waveform" write? Do they still sequence correctly and both play out?

3. What would be a scenario where you would want to sequence several effect waveforms?

I'm not really a software guy so I am having a bit of trouble locating the file that contains the definition of drv.setWaveform and drv.go.  Can you point that out to me?  Either Sparkfun or Adafruit example ok.