Groups are like folders; in that you can nest items inside them. This allows you to organize the contents of your proposal into logical, hierarchical groupings. For example, imagine a residential remodel project that breaks out scopes-of-work by Kitchen, Office, and Primary Bathroom. Each of these different rooms would represent an individual group.
Taking this one step further, within the Kitchen group, you could further break out your scope-of-work into groups by base cabinets, wall cabinets, and island.