Bacteria between teeth can cause dental decay between the teeth, gum disease, bone loss, and foul odor among other things.
Do yourself and other around your a favor. Clean 360 degrees around every tooth at least once every day.
In between teeth is favorite site to initiate cavities and gingivitis.
Floss every night before going to bed.
Brushing only cleans 3 of the 5 surfaces. Flossing cleans the other 2. Would you only clean 3 sides of your new car?
Yes, you have to floss your teeth twice a day. Most important is flossing before bedtime. Unfortunately, a toothbrush cannot clean between teeth.