50cc (actually 49.5cc) engines offer the advantage of being classified as a Moped or Scooter engine, and many municlities do not require a specific motorcycle license to operate a vehicles with engines sizes of less than 50cc.
Engines of exactly 50cc (or around 49.5cc) are categorized as either Mopeds or Scooters, and in most municipalities, no special motorcycle license is needed to operate these vehicles with engine sizes less than 50cc.