One example would modeling the costs and revenue for a business unit, the prices from suppliers, the fixed costs of capital, the number and type of employees, the throughput from sales, etc.

One of Excel's many powers is letting people play with numbers in cells and see the results of long chains of computations. Or create an array of potential values and see the results across a wide variety of inputs. Or even use the builtin solver to find the value that minimizes or maximizes a desired output...

And thats before starting on the pivot tables!!!