Invariably, I will create and distribute an Excel template only to fall victim to the dreaded formula overwrite offense. It's frustrating when a vacation schedule is returned that doesn't foot, or an item is coded incorrectly in an expense report after significant time has been taken to try and make a template idiot proof. Then some "idiot" spoils the whole thing by hard-coding a number over a formula.
Use the "Protect Sheet" option to help ensure that unwanted changes are not made into your Excel templates.
To illustrate, I have downloaded a template from Microsoft Online.