What's the benefit of getting the bigger A/R? Thanks!!

 

Are you talking about turbine housings?

Less backpressure, higher VE, higher flow.

Try the search.

 

Basicly it lets you set up turbos in between each turbine wheel size. A way to fine tune it to get the flow you want.

I don't really know how it affects compressors, but I assume it has a similar affect of fine tuning between wheels...