please make a search in CS for sRGB and (a)RGB and you will find tons of threads about it. You will find as well that the opinions are diverse and that the topic is controversial. You may also want to read what Ken Rockwell has to say and do a search on the net.
To make it short, most output devices (monitor, home printer, lab printer etc.) use sRGB. Unless you are very versed in colour management (switching from one colour space aRGB into another sRGB) use only one: sRGB.
aRGB is a bit bigger in most areas than sRGB but most of the time you do not notice the difference.