C12-15 Alkyl Benzoate is mostly used as formulation component. It gives the product a soft and silky but non-greasy feeling. As for the skin benefits, it's an emollient – it makes the skin softer and more hydrated. It also helps to kill bacteria and increase the product’s shelf life.
Fragrance is a mix of chemical ingredients (usually 20-30 chemicals but up to 200 sometimes) that help the product to smell better. It can hide many bad things. Synthetic fragrances may contain many different chemicals, but manufacturers don’t want to reveal each of them for some reason and hide them behind the word "Fragrance".