Can you explain the application for using only one worksheet in business?

The amount of worksheets you would use would be dependent on the complexity of the data you are working. You could have a very simple worksheet with a small amount of data, so that could be on one worksheet. If you are doing something more complex, you might decide to split the data for different parts onto other worksheets, like each set of sales figures for each region your sales staff work in being on its own sheet. You might have detailed income figures on one worksheet and expenditure on another and a final sheet with overall calculations. Much of the time though, you don't have something complex so it is sufficient to just use a single worksheet to do what you need to do.