Onion flakes are made from fresh onions that have been chopped and slowly dehydrated, concentrating their flavour. Onion flakes can be used to replace fresh onion and make a good emergency pantry staple.
Soup
Stew
Salad
Salad dressing
Garnish
Dip
Eggs
Rubs
Sauce
Sprinkle flakes on 
Curry
Pasta
Sandwiches and hamburger
Pizza
Onion powder is made from fresh onions that have been  dehydrated and ground, concentrating their flavour. It disburses evenly throughout the dish for rich, allover onion flavour. Commonly used as seasoning.
Soups
Stews
Creamy dips
Salad dressings
Casseroles
Vegetables
Rubs
Marinades
Onion salt
 
Natural benefits may include:
Onion contains sulphur, vitamins and iron which strengthen the nerves. 
Dehydrated Onions contain prebiotics, which improve sleep and even reduce stress
When the bacteria in the gut digest the prebiotic fibre, they can multiply and improve gut health and which release metabolic by-products.
Natural antibiotic
Anti microbial
Fights inflammation
Colds and flu
Breaks up mucus
Relieves sore throat and coughing symptoms
Heart health