Functional format is best for those who are switching their career or have large employment gaps on their resume. In this format, you dont have to list the joining or resigning dates of the previous employments. Functional format will hide your employment gaps or your job switching.
Your resume is your marketing tool for success. You need to be able to advertise your skills and ability to succeed with your prospective employer. The format and feel of your resume can either open doors or close them often this feeling can make people question why they didnt get the interview or thinking they are not qualified.
An attractive resume template/outline makes it more powerful. Just as dressing smartly helps a candidate in an interview good formatting does the same for a resume. Looks do matter at all places in the real world and on paper. When you present yourself well you get noticed. Similarly when you present a good resume it will be noticed; otherwise it would be very easily find a bin to rest in.