There are a lot of cases in views where you want to embed a list inside each row. One example could be, you have a list of groups, and for each groups you want to list the first and last name of all of their members. This can be achieved with this module, as views_field_view allows you to embed one view into another view and pass arguments along. It's highly recommended to use this module in conjunction with views caching. Views Content cache and Cache Actions are good ways of caching views.