I am not familiar with the US air industry, but I worked for a major Canadian airline until a couple of months ago doing mostly scheduled routes, but we had regular charter flights for oil and gas companies, hockey teams, private groups, etc. but our largest charter aircraft was a CRJ-100 that can accommodate up to 50 passengers. Other airlines in Canada such as Firstair and Canadian North do regular charters for mining companies, using ATRs, Dash-8, Boeing 737-Combi, Boeing 737-300s with a seating capacity of 136, and Boeing 737-400 that seats 135. When you want to go from point A to B as quickly as possible and you can fill the aircraft to capacity, chartering is the cheapest and most economical way to go.