We/me, as developers would need an (optional) audio feedback (beep, cling-clang) when the build was done, and the App is ready to start. (In Mendix Studio, when View App button is active)
The build can be a long process, lasting for minutes sometimes. At the same time we are browsing, watching something else, and not the building process - don't like to be idle, but use the time for something useful.