Why did workers decide to join unions positive/negative effects?

Workers joined unions so employers couldn't lay off as many pope and fire someone without God reasoning and they have to have a certain code this was really good for the workers because they got better working conditions, so it gives higher pay, and they couldn't get fired on a whim. A negative effect was that if the workers weren't happy then they would go on strike which was bad for business owners. 

Because they wanted better working conditions, It was good because sometimes they got what they wanted, it was bad because most of the time it didn't work very well and they didn't get paid.