Supported vs unsupported 3d prints

When a model has an overhang or bridge without being supported from below, you will more than likely need support.

Not all overhangs need support, overhangs built on an angle of LESS than 45 degrees can usually print without support.

When in doubt load your model into Cura and see if it will generate supports, if Cura does not place supports, then you should be able to print without support.