Any problems your smile has, or any nascent difficulties, will be caught early by your hygienist. Get a professional cleaning from your hygienist two to three times a year, more often if you've had a sizeable amount of dental work done. She'll find the plaque that you've missed, she'll scrape off the tartar that your brush and floss can't, and in doing this she'll help keep cavities and other complications away. Professional cleanings are like insurance for your smile. The investment can save you thousands of dollars in the long run, as smaller problems diagnosed along the way can prevent much bigger problems from occurring later on.
The purpose of a professional cleaning is not only to remove the tartar above the gum and bacteria-induced deposits below the gum as well as to polish off extrinsic stains from teeth, but to also get a comprehensive lesson in oral care. As she goes through each step of the cleaning process, your hygienist should explain what she's doing, why she's doing it and why your teeth may be sensitive or may start bleeding.
An adjustable mirror or an intra-oral camera (a more high-tech version of the mirror) is attached to the examining light, which allows you to watch your hygienist at work and understand what she's talking about. It's one thing to hear your hygienist say, "You really need to pay more attention to your back molars," but it's quite another thing to actually see her working on those back molars and fully comprehend what that work involves so you can replicate it at home.
Finally, based on the condition she finds your mouth in, she should give you an updated primer on the certain oral care techniques you need to incorporate into your home care routine.