You can use a Contract Addendum when you need to make minor changes to a contract, such as a change of date, or fixing or removing a clause.
If you need to make a major change to a contract, or the contract has already had several amendments, you might need to make an entirely new contract instead of using an addendum. Generally, a new contract should be created if it has been amended five times.
For example, if an employee is changing positions within the same company it might be tempting for the company to simply use an amendment to the employee's existing Employment Contract to save time. However, they may realize that the number of changes that need to be made (such as compensation, job title, hours of work, vacation time, etc.) might require them to create a new contract altogether.