Intra-Africa trade
In theory, it'll boost intra-African trade, but that depends more on the capacity of African countries to make what each other want at competitive prices, rather than a simple lowering or scrapping of tariffs between the 26 members.
The devil will be in the details of this agreement. There have been concerns over protectionist measures for local industries and a method of settling trade disputes.
But it may boost intra-Africa trade. At the moment, trade between African countries amounts to just 13% of total African trade. Some academics have said that this tripartite agreement could boost it by 30% over the next few years.
But there will be challenges on the ground. For a start, customs officials and getting across borders is notoriously cumbersome in Africa. Also, manufacturing on a local level needs to be boosted.