Depends what your doing.
To get useful info on wheel weights, you need to look up the exact model and size.
I've posted what I've weighed about 2/3 of the way down this page.
67 Barracuda Autocross Tech.
Doesn't include the 235/50R15 R888R since I haven't updated the website in while, but will give you a feel for the range.
Lightweight rims flex more. At some point the trade off isn't worth it, even for road racing. The flex effects the tire and in some materials eventually can cause cracks to develop in the rim
Steel rims can also fail. Scott Harvey recommended doubling up the centers for rally prep. The Hemicuda raced by Chrysler France broke one of the rally rims during an event. The car was run in a class that required stock equipment. They had been racing it at least a year at time of failure. The point is that under the repeated stresses of racing even a steel rim can break.
