Protection

Protection is applied at one of four levels: 

File-Level Protection: To control what types of changes people can make to a workbook, go to File - Info - Protect Workbook.

Workbook-Level Protection: Protecting a workbook means that users cannot view hidden sheets, add move, delete, hide or rename new or existing worksheets. This level of protection maintains the structure of the file.

Worksheet-Level Protection: To prevent other users from accidentally or deliberately changing, moving, or deleting data in a worksheet, you can lock the cells on your Excel worksheet and then protect the sheet with a password. Say you own the team status report worksheet, where you want team members to add data in specific cells only and not be able to modify anything else. With worksheet protection, you can make only certain parts of the sheet editable and users will not be able to modify data in any other region in the sheet. It prevents users from doing things within the sheet: format things, insert things, delete things, edit things, sort, filter, etc. 

Cell-Level: Modified through formatting. By default all cells in Excel are locked, but this has no bearing because the worksheet isn’t protected. To make some cells editable when the worksheet is protected, go to the protection tab in Format Cells and uncheck Locked. You can check Hidden to hide the cells when protecting the worksheet.

It is often necessary to protect either the sensitive information in one’s actual worksheet or the workbook structure from being edited and Excel’s four levels of protection serve to aid in that necessity.