Pros
Health care after one year, minimum hours required for coverage are guaranteed by union. Lots of locations if one needs to re-locate, transferring is usually not a problem. Slow and steady wage increases over time.
Cons
Wage increases are based on hours worked, NOT performance, so one gets paid the same as someone who doesn't work as hard. Increases are also very slow in the early going; 4 - 10 cent raises, then 4 - 20 cent raises, then 35 cent raises, then eventually 50 cent raises, etc... Most people starting at minimum wage trying to work up get discouraged long before the larger pay increases kick in. Department heads don't have the authority to raise their best employees' salaries up faster based on performance. They can only give more hours to some employees, allowing them to get raises more quickly based on the "hours worked" system.