Conti DWS Tire Pressure?
 

I just got my first set of new tires since buying my used 2009 A4, and after doing research on this site I chose the DWS's. Does anyone know what pressure I should be at? The midus I went to just put front at 35 and rear at 36.
I had my old Pirelli P6s at 32 front and 29 rear, as the audi manual recommended. Should I just put the DWSs to the same or do they require a higher pressure?

Assuming you are replacing with an OEM size, use the values shown in the manual. These are for normal loads for all brands of tires and listed by type and OEM size for driver and a passenger (all seasons in your case). The PSIs listed on the door pillar label is for max loads - 4 people and a full trunk. I usually start with the manual's recommendations and tweak up from there a bit to find the best compromise between ride and handling. In any case, you should not exceed the Audi pillar label's max psi despite what might be printed on the tire.

Based on the pressures, I take it you have 18". That's what I have.
I have 31500 miles on the clock and might need to change the tires before the winter. I drove them at 34 front and rear, but I noticed recently that there is more wear in the center, a bit more on the backs than the fronts and I dropped them to 33/33. The cornering traction improved, but I don't want to lower them more because they have soft side-walls and there is more leaning in the corners and steering imprecision than I'd tolerate. Given that I have never rotated these tires, I'm pretty happy with the mileage I got from them and not so happy with the cornering performance. I had my eyes on Bridgestone Potenza RE970AS for my next set as the best performing A/S tire at this point, but I changed my mind. The issue with those is the weight. To get this cornering performance Bridgestone has put a lot of steel in them - they are the heaviest tires in my comparison list. The Contis on the other hand are the lightest. I don't want to lose straight-line performance and I'm leaning towards Goodyear F1 Asymmetric as it's a tad heavier than the DWS, but its cornering performance is superb for this class and the winter performance is OK.

I actually have 17" rims. But I think I'm going to lower to 33 and see how it feels.
What are the benefits of putting less air in the bak tires?

Front tires usually require more PSI due to the car's front weight bias and steering/cornering.

If you look at the tire pressure sticker on the driver side door post you will see they put in the correct pressure for normal driving conditions. Less pressure will give you a smoother ride but will tend to wear the edges. More pressure will give you a harder ride and will wear the center treads. So pick your poison and either go with Audi's recommendation or play with your own.

You sure about that? Every Audi in at least the last several years states the door label is for max load PSI. Check tires pressures in your manual.

I agree. Use the pressures in the manual. I add a bit more for handling and leakage. Check and fill tires your self. Tire shops and service doesn't care. I have had 45 lbs. put in.

The DWS tires are light and weak. Avoid potholes. They are close to a snow tire in the winter though. At least the first winter.

What are the consequences of centre treads being worn vs the edges being worn

Uneven tread wear causing tires to need replacement sooner. Also, possible handling degradation.