Bacterias are the culprit that work against good oral hygiene. Most of the bacterias resides over tongue, some at the periodontal pocket and very little on the teeth. For this, tongue scrapping is the most important part of maintaining a good oral hygiene. But unfortunately, it's the most forgotten part also.
You always hear about brushing and flossing, but the tongue is far too overlooked. The tongue is the main cause for bad breath. I think because people think about cavities so much, the idea of tongue bacteria never crosses the mind.
Very true - i always brush/scrape my tongue after brushing teeth and then a good old gargle. There are even tooth brushes that have a scraper on the back of the brush head - so there is some awareness of this although it is def the exception.