When creating financial models / analysis in excel spreadsheet that you intent to share with others, it is good practice to protect excel spreadsheet from unwanted changes.
You can control what a user will update. For example, look at the image below. This is a yearly budget worksheet. I always format input cells in blue color font to clearly tell a user what needs to be updated. You can see that a title and account categories can be changed; and full year budget estimates should be updated. Then, monthly distribution will be automatically calculated depending on the parameter that will be selected from the list.
To make sure that the formulas are not overwritten, I protect all cells in spreadsheet except those formatted in blue font that I want to be updated.
To do that, you first need to unlock protection in cells that you do not want to be protected, in my case all cells formatted in blue color font. Highlight all of cells that you do not want to be protect, then go to Format / Cell / Protection and uncheck locked check box. Click OK. Now you ready to protect your spreadsheet; go to Tool / Protection / Protect sheet and make your protection selection. To unprotect go to Tool / Protection / Unprotect sheet.