Flossing is important to overall oral health.

Even by itself, flossing does a good job of cleaning teeth and gums,
and is the only way to clean below the gumline.

However it has an important secondary purpose as well. Most people assume
the point of brushing teeth is to scrub the teeth with bristles. This
is not fully true; the more significant purpose of brushing is to apply
fluoride to teeth. If you don't floss, food particles are left between
the teeth and gums, blocking fluoride from reaching tooth surfaces. It
is then as if you were not brushing at all. Even if no material is
visible between teeth, there is probably some there. Flossing can pull
a surprising amount of gunk from a mouth that appears totally clean.