Personally, I run 20g in the front under the servo and 15g around the receiver. The front weight is to try and keep the front end down under acceleration and the 15g around the receiver helps to balance out the speedo because I run the small KO's. Other than that I haven't found a need for weight. The total weight of my car was around 1500g last year, but was as low as 1474g at some points
On the other hand, plenty of people do run more weight, and it will make the car easier to drive for the average racer. In my opinion this makes it slower for me, hence I don't run much.