What is DelayValidation and what is the significance?

During early validation all of the components of the package are validated along with the package itself. If any of the component/task fails to validate, SSIS will not start the package execution.

In most cases this is fine, but what if the second task is dependent on the first task? For example, say you are creating a table in the first task and referring to the same table in the second task? When early validation starts, it will not be able to validate the second task as the dependent table has not been created yet. 

Keep in mind that early validation is performed before the package execution starts. So what should we do in this case? How can we ensure the package is executed successfully and the logically flow of the package is correct? This is where you can use the DelayValidation property. In the above scenario you should set the DelayValidation property of the second task to TRUE in which case early validation i.e. package level validation is skipped for that task and that task would only be validated during late validation i.e. component level validation. 

Please note using the DelayValidation property you can only skip early validation for that specific task, there is no way to skip late or component level validation.