Feb
In a nutshell, that person is responsible for the type of business that division/affiliate/subsidiary handles.
A clearer illustration would be to use railroads. Given the kinds of traffic a railroad would handle, it would be logical to divide the business units along those lines. For example, if the railroad handles coal, lumber, intermodal and automobiles, there likely would be separate unit heads to oversee that traffic. Each of these unit heads is responsible for marketing, sales, etc., for that industry or commodity. (When I worked for CSX, that’s how things were structured.) Ultimately, those unit heads would report to someone higher up, say, an executive vice president.
My girlfriend, who spent years in the hotel industry (including eleven at Walt Disney World) states hotel chains would also be similarly organized. Depending on the specific chain, they might have unit heads for corporate/business sales and for families or vacationers, to help manage the marketing and so forth for those areas.