This feature looks like a must for some developers. Here's the reasons why:
1) Some companies on other countries may copy your game and change the advertisement keys in the game. They basically steal your work and make money over you and they still use your PlayFab title, which can be a huge problem. Since PlayFab has consumption-based pricing, it can affect the billing.
A solution can be banning those players, however, it still affects our analytic data. Furthermore, removing those players from the title spins the read and write meters, which can be expensive depending on how many users there are.
Whatever solution we make on our sides, it can be expensive. Blocking a specific country is easy to solve this issue. IP addresses are estimated and it can accidentally block wrong players or players can use VPN, but still, some developer might want to take those risks.
2) Some developer may want to target a specific country or countries. With the feature, the developers can block the other players easily.