It let you support multiple online services using same code without much of modifications, it also let you use online services in blueprint too without need of C++. Documentation is kind of poor right now but here blueprint achivment example for stream:
UE4 APIs is design in the way so you don’t need to talk to system or external libraries, UE4 has wrappers for many things which improves portability and UE4 APIs are huge, lot of things that you can miss easily, so try to search first or else you might go harder way for no reason.
But for the future, if you really want to include external library here tutorial how to, UE4 use own build system UBT and don’t listen to VS configurations but build scripts (C# code you got in source directory):
So I have my Steamworks SDK imported in my Unreal Engine project. It builds, and on run, I get the Steam overlay. Great!
However, I am now trying to get the user’s friends list, which requires the Steam Community API, which is included in two files, ISteamFriends.h and ISteamUtils.h. I am trying to import those into an Actor class that I created to manage Steam communication, but Visual Studio doesn’t see the files and won’t build.