Why do we actually compost?

Why do we really compost? I learned so much about why #FoodScrapsArentGarbage while producing this video with @MetroVancouverBC.
 
Also, did you know that a lot of plastics marketed as "compostable'' or “biodegradable” don’t go in the green bin? For example, the “biodegradable" plastic liners sold for compost bins often don't actually break down enough in Metro Vancouver's composting facilities! To play it safe, it's best to just line your green bin with paper bags or newsprint.