The Bachelor of Advanced Studies is an additional year that you can complete on top of a Bachelor's degree (in this case, the Bachelor of Economics). As part of the Bachelor of Advanced Studies, you can choose to either take advanced coursework units or complete an Honours year. In other words, the Bachelor of Advanced Studies allows you to delve deeper into a particular field. In the case of the Bachelor of Economics, completing a Bachelor of Advanced Studies would enable you to learn more about Economics, whether it is to use that knowledge within your future career, or undertake further study, such as through a PhD.
On the other hand, completing a traditional double degree, such as the Bachelor of Economics/Bachelor of Arts means that you would be gaining knowledge and skills across two different fields (in this case, economics and arts). A double degree typically increases employment opportunities given that a graduate would be able to work in two fields as opposed to one. In some cases, a graduate may use the knowledge and skills that they gained from both degrees in their career. This may be the case for a person who studied a Bachelor of Commerce/Bachelor of Laws for example. At the same time, you would study a double degree in less depth than a single degree with a Bachelor of Advanced Studies.
I hope this helps!
