Why should it help laundry to add vinegar to it?

http://tipnut.com/laundry-boosters-vinegar
  1. / Color Brightener: Add 1/2 cup vinegar to a load of laundry (wash cycle).
  2. / Color Protector: Soak new items in a straight solution of vinegar to protect dyes from running.
  3. / Whiter Whites: Add 1 1/2 cups of vinegar to the rinse cycle to whiten clothes.
  4. / Restore Whites: Fill a large stock pot half full with water and 1 cup of vinegar, bring to a boil. Remove from heat, add garments and let soak overnight. Launder as usual.
  5. / Preserve Linens: Add 1 cup of vinegar to rinse cycle, store linens as needed–will help prevent yellowing.
  6. / Yellowed Items Reviver: Revive old yellowed garments & linens from storage by soaking overnight in a solution of 12 parts water to 1 part vinegar. Launder as usual. Also see Cleaning Vintage Linens Recipe and Cleaning Vintage Linens Soak.
  7. / Heavy Duty Pre-Soak: For heavily soiled garments, first soak in a bucket of water with 1 cup of vinegar. Launder as usual.
  8. / Lint Busters: Add 1/2 cup vinegar to the rinse cycle to reduce lint.
  9. / Fabric Softener: Add 1 cup of vinegar to the rinse cycle. Also see Frugral Fabric Softener Recipes & Dryer Sheet Tips and How To Make Wool Dryer Balls.
  10. / Ring Around The Collar Remover: Use 3 parts baking soda to 2 parts vinegar to make a paste, rub into stain and allow to set for 60 minutes, launder as usual. Also see Quick Tip: White Collars Trick.