While I've trained new pilots and flown demos with non-rated individuals, I've never flown one with the opposite seat empty. Several emergencies in critical modes of flight are easier/safer when handled by a crew of two or more. Engine failures, fires, governing problems along with hydraulic/flight control malfunctions occurring at inopportune times could quickly lead to pilot overload, and respect the dreaded multiple emergency situation too. However, if properly trained, all but the worst situation could probably be survived by a competent single-handed pilot. Remember to consider visibility, mission and environment. While almost any decent pilot could solo a UH-60 on a day VFR hop between two airports, don't forget to think in terms of an NVG sling-load off a hostile Afghanistan mountain top in a snow storm.