Storing your data in the same place you plan on analyzing it seems logical. For instance you have a spreadsheet of sales figures that needs some formulas and statistics. So you collect all the data from the sales staff and build a great spreadsheet that contains the data, formulas, charts and analysis.
Consider instead storing the data in a SharePoint list, exporting a linked copy of the data to Excel, then building the formulas, charts and other analysis around the exported data. The great thing about this approach is when the data in the SharePoint list is updated, the Excel file can be updated with a single click. No more transferring data from email, post it notes, word of mouth, into the spreadsheet. Now we get all the data from one source: SharePoint.