The biggest drawback in using server-side validation is that the validation occurs after form submission. This means that if any validation rules fail, the user must go back to the form, make the corrections, and resubmit it to the server. To make matters worse, some browsers lose the data in the form fields when the Back button is clicked, forcing the user to reenter all the data.
Obviously, this hardly creates a user-friendly interface. Too many good Web sites have lost visitors because their forms were aggravating to work with.
Fortunately, an alternative is available: client-side validation.