Progress bars are horizontal bands that show the degree of completion of a task or process. They give a quick indication of the current status of, for example, projects, tasks or budgets, which can be useful for checking how close a task or project is to completion or if a project is coming close to hitting its total allowed budget.
Progress bars can be especially useful in large projects that consist of multiple smaller projects, as you can display within one element separate bars showing the degree of completion of each sub-project and of the main project, giving you an overview of progress at a single glance. Separate elements within the diagram can contain further progress bars for the metrics of the individual projects, adding levels of detail that can, again, be assessed in a brief review.
In Enterprise Architect, progress bars are implemented using Tagged Values on elements.