Butt emissions: Study finds even extinguished cigarettes give off toxins. Researchers have discovered that a used cigarette butt - even one that is cold to the touch - can give off the equivalent of 14% of the nicotine that an actively burning cigarette emits. They are calling this newly discovered form of cigarette exposure ''after smoke'' or butt emissions. Source 6r.
Anything from a cigarette can simply be a pose a certain risk in the first place. Even after you're done with the cigarette the smoke and heat still remains - hence why sometimes you must completely extinguish the item because if dropped to random spots it can literally cause a fire in some cases!