In trying to follow a sketch for writing hello world, I got stuck on a line that said
display.begin(SSD_1306_SWITCHCAPVCC, 0x3C);

In the ssd 1306 128x64 example, about 1/4 of the way down the code (I haven't figured out how to turn line numbers on yet) it says :

// by default, we'll generate the high voltage from the 3.3v line internally! (neat!)
display.begin(SSD1306_SWITCHCAPVCC, 0x3C); // I corrected this to 0c3C from 0x3D (for the 128x64)
// init done

In the adafruit ssd 1306 library on line 150 it says :

void begin(uint8_t switchvcc = SSD1306_SWITCHCAPVCC, uint8_t i2caddr = SSD1306_I2C_ADDRESS, bool reset=true);
void ssd1306_command(uint8_t c);

Amazingly, I could find nothing about this on Google. I don't get the drift of the 'HIGH VOLTAGE', nor what is 'neat' about it. And can't I eliminate it (no luck trying so far) ?

I think I partially figured it out. It seems to set the power source type.