Corn Harvest From the Cab.

I grew my own field of corn this year but I harvested it much earlier when the corn stalk was still green but the bottom leaves were brown. This I'm told is the correct state to harvest the corn in cause it's still sweet and if I waited longer the corn would lose sweetness. But I've noticed that some of the the farms around me waited till the stalks were basically brown and dead looking to harvest. What's the deal? Are you harvesting it for fuel or something?