lets all be honest.. they are their to look cool and that is it..

or in some cases their to make u look a chav
the audi's look absolutly awesome and nobody can say they dont, just as the BMW's did when they first introduced the halo head lamps, now every chav has angel eye headlights

as said before...use your sidelights if visibility is reduced at all...
the only other good thing about them i guess is the fact they draw less power than your sidelights with them been LED..
then again, u may as well do the xenon upgrade like i have instead, uses less than half the power of your crappy halogen bulbs....
it comes down to a personal thing, i love the audi's....but i wouldnt bother retro fitting them instead of my fog lights as i prefere a OE look, just my personal taste