As a business grows it gains two major advantages over its smaller rivals. Large firms have more influence over market price. They're big enough to be price setters.
Large firms also often enjoy economies of scale. This means that a business has lower unit costs because of its large size. They can buy raw materials cheaply in bulk and also spread the high cost of marketing campaigns and overheads across larger sales.
For example, if a large firm can produce a given type of sunglasses for £20 while it costs its smaller rival an average of £30, then the larger firm has a £10 per unit cost advantage. Larger firms can charge lower prices or enjoy a higher profit margin.
Economies of scale are a major source of competitive advantage for large firms.
A business can grow in size through: