ADC and Timer relationship in DUE

Official Hardware Mega Due
4

I had a look at some more examples, but I still cannot figure out, why some people are using ADC in free running mode and setting timers as well. What is the purpose of that?

Here is a sample code. IT IS NOT MY CODE. I just found such one.

//timer library
#include <ARMtimer.h>
#undef HID_ENABLED

int result = 0;

int sampleCount = 0;
int sampleFrequency = 100000;
// unsigned long sampleTime = 1000; //in millis
const int numSamples = 2048;
int resultArray[numSamples];
unsigned long programtime = 0;
bool once = false;

//setup adc function

void prepareADC(){ 
	
  pmc_enable_periph_clk(ID_ADC);
  adc_init(ADC, SystemCoreClock, ADC_FREQ_MAX, ADC_STARTUP_FAST);
  adc_enable_channel(ADC, ADC_CHANNEL_7); 
  ADC->ADC_MR |= 0x80; // free running
  adc_enable_interrupt(ADC, ADC_IER_DRDY); 
  NVIC_EnableIRQ(ADC_IRQn);
  adc_start(ADC); 
}


void ADC_Handler(void)  {
	//Check the ADC conversion status
	if ((adc_get_status(ADC) & ADC_ISR_DRDY) == ADC_ISR_DRDY) {
		//Get latest digital data value from ADC and can be used by application
		result = adc_get_latest_value(ADC);
	}
}

volatile void receivedata()
{
	if (sampleCount < numSamples){
	   resultArray[sampleCount] = result;
	}  
	sampleCount = sampleCount + 1;
	if (sampleCount == numSamples){
	  sampleCount = 0; 
	}
}


void sendData(){
  for (int j=0; j<= numSamples; j++){
	  Serial.print(j);
	  Serial.print(": ");
	  Serial.println(resultArray[j]);
  } 
}


void setup() {
   Serial.begin(115200);
   prepareADC();
   programtime = millis();
}

void loop() {
  	delay(2000);
	int now = micros();
	startTimer(TC1, 0, TC3_IRQn, sampleFrequency, receivedata);
	sendData();
	stopTimer(TC3_IRQn);
	int dur = micros() - now;
	Serial.print("dur: ");
	Serial.println((float)(dur/numSamples));
	sampleCount = 0; 
}