Reports can be used both to see detailed statistics on your incomes, expenses, assets, etc. than printing documents concerning a specific period of time and specific accounts
Profit & loss report is perfect to declare incomes and expenses for a little business for a tax return. The piechart is great to identify which incomes or expenses are the higher or lower.
The bartchard let you see the evolution of your incomes and expenses on a time line, which is also pretty useful.