The phrase “It’s peanut to XXX” means “it” is of little value to “XXX”. How peanuts came to mean something insignificant is not clear, but the legume itself is definitely a prized crop. Peanuts, also known as groundnuts, have copious culinary uses. From a cooking medium to a snack to flavouring ingredient, it is favoured in Africa just as much as it is in Asia…
 

Peanut as cooking medium
 
Deep fried recipes such as American southern chicken or French fries almost always call for peanut oil. This is because the oil reaches very high temperature (over 200 degress Celcius) that makes the outside of the food crispy and the inside moist. Peanut oil also imparts a subtle nutty flavour to the food.
 
Peanut as snacks
 
Peanut candy, especially from Jin Men, Taiwan, is popular amongst the Chinese in this region. Roasted peanuts are mixed with malt sugar, then blended, flattened into sheets and folded into blocks of sugary goodness.
 
In United States, raw or freshly harvested peanuts are used to make boiled peanuts. They are boiled shell-in in salt water till soften and savoury. Likely the slaves created this snack as early as the late 19th century when they had surplus peanuts (the first recipe for boiled peanuts appeared in 1899).
 
Peanut as flavouring ingredient
 
Roasted peanut is eaten on its own or used as a flavouring ingredient in various Asian dishes. Crushed, and sometimes sugared peanuts are often found sprinkled on noodles (think pad Thai or Hainan noodles), rojak, stir-fry vegetables, as a spicy peanut dip in satay etc. They also add crunch to the dishes.