Spreadsheets are a very common method of producing test data im many organizations. Many of these spreadsheet testing schemas are very complex and can involve many cross references to other sheets as well as formulas that are generally hidden behind the value that the user sees.
It is important to note that with DataFinder, the formula's "may not" import and may actually "choke" the import job. (yes, I realize that is not a sophisticated technical term, but it conveys the end result)
Best practice is to copy the sheet to another sheet with "values only" and then use that "values only" sheet to import.