Use this web block if you want to show a visual information of your process. Imagine you are uploading 5 files and once they reach the server and you start processing them, you want to show in the UI some kind of information like "Processed file 1 of 5"...... "Processed file 2 of 5" ... and so on and so on.
This visualization is implemented using a modal dialog and the user cannot interact with the rest of the UI.
You can control the modal's title when opening the modal. You can also control if you want a progress bar. This type of visualization is useful if you want to show the progress with a more graphical visualization.
And you can also control the text, giving some more contextual information of what's happening ("Processed file 1 of 5")
Important: this only works with AJAX action calls. This uses the RunJavascript action, so this only works if there is a web context. You can use this on any module, but conceptually makes more sense to use on screen actions or actions from the front end module. No problem using on actions that belong to business layers modules, the thing is, if these actions are used on timers, BPTs or emails, there is no web context so this module and their actions will not work.