What is the function of the heavy hex head on a heavy hex bolt?

What is the function of the heavy hex head on a heavy hex bolt?
Bearing Surface Heavy hex head has a larger bearing surface. For example a 1" heavy bolt 1-5/8" dimension across the flats. A finish hex bolt is 1-1/2". This creates a strong fastener. This is one reason many high strength structural bolts like ASTM A325 and A490 are specified a heavy hex pattern.

Head Height The head thickness is identical for both bolts.

Application These bolts are often found in industrial and steel connection situations. The stronger design is critical.