The reports section gives you an over view on your sales AND expenses. Sales totals are broken down by total (payment amount), tax, shipping, credits and discounts.
You can also keep up with your general business expenses in Sytist. Entering in your expenses in the Sytist admin lets you see your total sales and expenses for the year at the same time.
When adding expenses you can create labels. This allows you to see your expense totals by labels (or categories).
You can add an expense from the Reports section AND you can add an expense when viewing an order. Example, you have an order for prints and you receive your prints from the lab, you can enter in that expense to the order and it will show in your expense reports.