Applications are often formal documents that offer little space to elaborate on your skills and abilities. Remember that every person applying for the job is filling out the same generic document. Applications often do not allow you to set yourself apart from your competition.
A resume offers you the ability to be unique and keeps an employer interested in your application. It gives you the space to elaborate on your qualifications, work history, and education. It also can show the employer that you are taking extra time to update and submit a resume to further explain your qualifications.
Although, applications are a vital piece of the application process submitting a resume may help you secure an interview.