It gives research points, which helps towards westernization as well as 2 prestige and lowers militancy by 1. It also gives cores on the 3 states Amhara, Oromia and Eritrea. Amhara and Oromia are partly owned by Ethiopia, partly Uncolonized. Eritrea is partly owned by Egypt and partly uncolonized.
Only Egypt can initially be attacked with the return cores casus belli, and nothing can be done about the uncolonized provinces.
The provinces that are uncolonized will usually be colonized by European powers, and they can afterwards be attacked. It may however be difficult to retrieve them.