I use of both Python (pandas) and base SAS at work for UK government. I have lots of experience in SAS, and enjoy using it. The macro language allows for very succinct solutions to difficult data manipulation problems. However, given SAS's huge expense it's difficult for me to identify any 'killer' areas where it's significantly better than open source tools. Indeed, I find pandas faster and easier to use for many pr…
I'd say SAS's two big "Killer Features" are the DATA step and SAS Press. I still have yet to find R or Python nearly as pleasant to work with for manipulating the data set itself when compared to SAS, and the SAS Press is excellent at putting out books detailing a given type of analysis, and how to implement it in SAS. I still turn to them for basic references even when not using SAS.