Why do we need 3 lights as DRL? Isn't it too much of power consumption?

The DRLs on the 450 is actually pilot lamps and do not qualify as DRLs. Hence, it is mandatory to keep the headlamps on. As for the energy consumption, at max(high beam) the power required is about 8W, so if they are kept on for around 4 hours, they will consume the equivalent of a km worth of range.