Why upgrade some LED headlights need to add decoder?

Since the power of the original halogen lamp is generally 55-60 watt, and LED headlights' working current and power are smaller, (most of car models on the market do not need to decode, or they built-in decoding) some car models' original headlight control line through driving computer will by default fault, then will start the alarm or the headlight flashes. So you need to add a decoder (actually a decoder is a resistor) to process it.