Hi.
Github allows developers access to the UE4 source code…This allows folks to make modifications (and bug fixes) to the actual game engine. This is useful for really smart people so they can apply certain commits (which is code changes) to their engine. So, let’s say I have a branch from 4.8 and there is some sort of bug that was fixed in 4.9, BUT, you don’t want to upgrade the entire UE4 system to 4.9 because you project might break, you could simply install the patch (commit) that fixes the issue.
If you do not know C++, I would suggest you stick with the binaries from the launcher.
BUT, if you want to play with new features before the binaries are released, that would be another reason to use github.
This is a little outdated, but this information should be helpful…
teak