Groups can be created in the Contacts (Individuals & Organisations) and Deals sections.
Groups can be viewed in a basic list view, or a more comprehensive table / report view.
Common uses for groups include
Reporting on Sales, Leads, Pipeline, Contact Data
Sending Email Campaigns
Filtering the Deals section (Deal Groups only)
Analyzing lead quality (Marketing Dashboard)
Creating call lists (Telesales Dashboard)
Exporting and printing information in spreadsheet format