To protect your spreadsheet, Excel proposes the following options:

Usually you can view a formula in the Excel cell when cell is selected, but you can protect spreadsheet to hide formulas in some cells.

Sometimes you might want to lock cells in your Excel spreadsheet that contain formulas and functions or data. Thus, the person doing the data entry will not accidentally overwrite or delete the spreadsheet formulas and functions or your data.

You can significantly reduce the number of errors in data entry in Excel by protecting changes of specific spreadsheets (worksheets) and cells.

Much like as you can protect elements of each Excel spreadsheet (see Protecting spreadsheet elements for more details), you can protect structure of the sheets in the workbook, prohibiting renaming, moving and other operations.

With Excel built-in tools you can easily work together on workbooks and monitor who, when and what changes made. E.g., track project status and tasks.

Working with large and complex Excel workbooks, especially when entering large amounts of data, no one is protected from accidental changes in formulas, formats and other spreadsheet elements. But you can protect yourself from too much work on finding and eliminating such errors by protecting the individual spreadsheet elements.

Excel offers you an ability to assign user-level permissions to different areas on a protected spreadsheet. You can specify which users can edit a particular range while the spreadsheet is protected. As an option, you can require a password to make changes.