PaulS:
even in tutorial there is LED stuck in pin 13 without any resistor
That doesn't make it right. We've been trying for years to get the team to fix that.
An LED draws as much current as it can. That can damage the Arduino. A current limiting resistor limits how much current the LED can draw, protecting the Arduino.
Use them or plan on replacing the Arduino when the pin quits working because it has been abused too often. Your choice.
Sounds logical, will do. Thanks for explanation.