Applications are sent back for very, very minor deficiencies, something like you missed a box or your photograph was the wrong size, things that could easily be rectified.
My recommendation would be to send an email or call the applicant and tell them to replace it, instead of sending the whole thing back. Not only does that result in delay and extra expense to the client having to do it all over again, but it also sometimes leads to a loss of substantive rights. That means that somebody may fall out and lose status while that application is been sent back, and now they're here illegally. Or, you could lose the right to sponsor somebody, for example, your child ages out in terms of the date for sponsorship.