The build process drops the build database if it already exists so it can build it, the drop will fail if there are other current connections to the database. ForceKillBuildTarget will disconnect them with SET SINGLE_USER WITH ROLLBACK IMMEDIATE then drop.
DropDBIfExistsForCpyDB: controls whether the copy process drops the target if it exists.
EnableCustomScripts: Primarily enables the screens in the GUI wizard that allow you to configure custom scripts to run at various stages of the processes.
Recommend familiarising yourself with all the GUI before looking at the settings files. If you know hoe to use the GUI and what how it behaves it makes understanding the settings file easier.