The temperature of that bare concrete floor will be pretty cold in the winter (45 F? maybe). If you intend to heat the space, doing something to reduce heat losses there will save money in the long run. And, a little insulation there will reduce the heating bills in the rest of the house, as it is probably a major source of heat loss if the bottom of the first floor isn't finished. If the bottom of the first floor is fully insulated, then the heat loss to the rest of the house is a minor issue.

You can use a "subfloor panel" which is osb with a plastic spacer to stand it off the concrete, or build your own with some high density foam, pressure treated sleepers, and a plywood floor.