What is the point of side lights?

Up to quite recently there were large notices in the Mersey Tunnels instructing drivers to turn off headlights. Many drivers now turn on headlights in the tunnels (or have auto lights) but in heavy traffic the dazzle is considerable. However you do need the parking lights on to see the instruments when in the tunnels.

Incidentally all bus drivers in Wirral are instructed to turn their headlights on when leaving the garage both day and night.

On another point, IIRC, motorcyclists were very opposed to cars having their headlights on all the time as they reckoned people would therefore not be able to spot motor bikes with their headlamps on - work that one out!