Using a functional resume format is beneficial when you have gaps in employment. The functional resume highlights honors and achievements more than work experience. It lists your skills and other attributes that make you a good employee at the top of the resume. It is important to fill the gaps in employment with experiences that helped you grow. Volunteer work, continuing education, and other projects you worked on during that time are all great options. Be sure to use a positive tone while describing the gaps in employment and be confident about them when interviewing later.
However, this is a case where you’ll want to use your common sense. If you went to college for marketing and had a marketing internship your senior year, then worked as a server for the next several years, you would want to include your marketing internship.