Your glutes are the biggest and strongest muscles in the body, and your thighs can hold their own, too. Movement is nearly impossible without your core doing its job. So it stands to reason that working these major muscle groups should be a high priority. Not surprisingly, a lot of specific exercises do double- or triple-duty, working more than one area at a time.
The three body areas personal trainers are most-frequently asked about are the abs, butt, and legs. People, especially women, want trimmer, plumper, and more slender in these three areas.