We use both, and both would have occurred historically. On the Plains of the Central U.S., people have been here as long as prairies have (since the recession of the last glaciers and subsequent development of grasslands). Those people used fire frequently and with multiple purposes. More importantly, we use fire today to achieve particular objectives and don't worry over much about whether we're burning at the same time a site would have burned historically. Instead, we are trying to figure out how to manage for biodiversity in the face of rapid climate change, invasive species threats, nitrogen deposition, and many other factors.