Snow for one, which is the main reason why I'm doing it. Plan to move into the country side in the life time of the car and don't want to get stuck. Also better holding on muddy roads.
I've been driving a DSG Altea for nearly 12 years. The DSG is fine, but on snow it's looses traction on slight inclines. You won't get that with a 4WD. It isn't the DSG doing it, but you can in the 2WD release traction control to stop it messing about. That's a traction control thing.
I have sneaking suspicion that a 2WD DSG Ateca wouldn't have behaved like my Altea, perhaps less power in 150....haven't done the sums, but wouldn't have fixed the snow issue. There is a band of anti 4WD people that say, no, 4WD isn't the solution, deflate the tyres, snow chains and blah, blah, blah. You see that in the Telegraph motoring pages. Where my brother use to live he was stranded in his village till the 4x4 owners cut a path out and with wear it melted and you could get out with a 2WD. Don't want to be in that position myself. I'm country boy that moved to London, but I'm doing what the monied types do that live in the country when I make my return.
DSGs are wonderful things at saving arm ache by constant changing up and down. On the M25 and M1 round here they are a joy.