The major advantage of union strikes is that they allow workers to protest action by an employer that they feel is unfair without the risk of firing or punishment. A disadvantage of strikes is that they can cause financial damage to the company involved since no work is being performed.
Labor strikes are a useful tool for a union when it negotiates a new contract or better working conditions for the workers whom the union represents. Striking protects workers from unfair action being taken against them when they speak out against unacceptable working conditions.
On the other hand, labor strikes can negatively affect many people beyond the company involved, explains How Stuff Works. For example, the 2005 New York City transit strike caused the shutdown of one of the world's largest transit systems for two days, leading to trouble getting around the city for millions of residents.