Do I need to filter POST in this case?

Question

PHP

Such situation. The user fills out the form and sends it to the server. I check all incoming data and if an error is found somewhere, I need to return the form with the data that the user entered into it.
The server generates the form and puts $_POST['title'] as the value parameter in the type="text" field.
Do I need to check/filter $_POST['title'] again?