Validation rules are an important tool in Salesforce. In a nutshell, they verify that the data entered into a record meets specific standards before the user can save the record. Taking it a step further, validation rules can be applied to give specific permissions to specific users. These can be used to enhance security settings to ensure that specific users, or groups of users, are only able to edit specific fields or perform certain operations.
Some examples of this are: setting limits on discount amounts, limits on expense amounts, and making certain fields editable by only the record owner or administrator. To create these user based validation rules, simply go to your validation rules screen and add the proper validation code to whichever field you want to manage. See the link below for some sample formulas!
-Ryan and the CMB Team