sometimes parking lights are used to illuminate the rear lights so others know theres a car there. or to illuminate the dash lights only to see the speedo better etc etc 
both my cars have  fog/driving lights with the Hyundai even having a set for the rear lamps (yes rear fog lamps, illuminates red and is independently switched as well)
on both vehicles, the driving lights/fogs or whatever you want to call them ONLY illuminate the sides and the very immediate front of the car.
if the driving lights are switched on and off while the main headlights are on you can see a small change in the lighting around the front sides of the vehicle and immediate front.
i use both sets of lights at night always as they dont blind anyone and are very small ouput (27watt i think) and are independently switched.
i dont see anything wrong in using them how i am.
 
cheers

Fir enough about illuminating the dash lights, but if its dark enough not to see the dash, I would say its dark enough to not be seen properly, so turn on your lights.  I generally drive with lights on all the time (so I can be seen), its a habit from driving subarus where you can leave the lights switched on and they turn off with the ignition, brilliant functionality.
 
Please tell me you dont turn on your rear fog light unless its foggy!!  :)  They are blinding to people following and make the brake lights much less noticble.
 
Thats my rant for today!!
 
Cheers

i find that sometimes i have to turn on the driving lights to have a proper view of the speedo but it isnt dark outside yet. so i just use the parkers (along with the driving lights)
 
im sure all new cars have the lights out function when the keys are taken out even my hyundai has it lol
and yeah i use the rear fogs when i remember at night. its not blinding at all and the stop lights are quite noticable when brakes are used as they are a seperate light again.. ive checked them all and dont see any reason not to use it for safety purposes. if they were confusing to look at from behind i wouldnt use it but thats not the case here.

Tree

Is driving with fog lights only on the freeway okay? Just to save fuel 

 
Nah, that would get you two tickets, one for 'use auxiliary driving lights when not permitted' and 'drive during period of darkness without prescribed headlights' - apparently. 

Oddly, not all new cars have auto off lights, though most beep if you leave them on to spare a flat battery.
 
Cheers