USB To RS232 TTL pinout?

I just bought one of these to read the raw serial output from my Arduino. It seems pretty straight forward to connect, just TX, RX, and Grnd?

Why does it also have a VCC pin and a 3.3v pin? I'm assuming it has an alternate use outside of just reading serial output?

It looks like it can supply both 3.3V and 5V power to your project if needed. Don't connect these if your arduino is powered from another source though.