I have this circuit:
simulate this circuit – Schematic created using CircuitLab
And I would like to understand why I need a limiting resistor for the current flowing through D1. I know the theory is quite clear, Ohm law tells me that if I don't have any resistance, the current will be infinite. But in this case I can limit the current by controlling the base current of Q1. I did some experiments at home, I did the calculations, I built the circuit on my breadboard and actually the current flowing through D1 was the expected (13mA in my case) without installing any resistor.
So, what am I missing? Do I need a limiting resistor? I am asking this because people keep telling me I definitely need one, and I don't understand why.