What is the advantage of making a separate Installed build over simply checking-in binaries in the engine directory?
Installed Builds are better when working on a team, as they enable your teammates to work without needing visual studio.
Furthermore, the VS workspace created for a project using a non-installed engine seems to have difficulty determining dependencies - you often end up unnecessarily rebuilding the engine even for game code only changes ( at least in my experience)
From a technical standpoint, an Installed build contains precompiled binaries for Unreal Editor and a static library for each target platform in development and shipping configurations.
It saves tons of time that can easily be wasted otherwise (accidental full engine rebuilds)…