"Use dipper"

I am sure most of you must have seen the road sign, "Use dipper at night".
Now lets analyse this a little. First of all, I hope everyone here understands the fact that dipper can only be used if you have your headlights on. With that fact in place, the question is, why does it have to specified that dipper is to be used at night?
Unless you are in a Scandinevian country (where its compulsory to keep your headlights on even during the day because of the fog), or theres a solar eclipse, we can safely assume that most of us, who have the tiniest bit of common sense would not be driving around with our headlights on during the day.
Hence, wouldnt just "Use dipper" serve the purpose. Just think of the economic implications if this was how it had been written in the first place.
Half the paint, half the no. of manhours, smaller board. All this saving multiplied by the number of such boards in the country. Got to amount to something. Like one meal for someone?
Comments welcome.
PS: btw I hate people who drive with high beam even if theres oncoming traffic.