The main goal of the Widget concept (introduced in Qlik Sense 3.0) can be described as follows:
Allow users to create new visualizations for Qlik Sense without the need of having any programming skills.
Widgets are best suited for creating simple visualizations, such as KPI objects, tables or any other kind of simple information representation.
Widgets can also be used to add simple actions to objects, such as buttons to clear selections, to jump to a different sheet, or to add other visual elements.
To make it even easier to create widgets, Qlik Sense provides a powerful development environment to create and maintain widgets: The Widget editor