Vantaggi
They often require evening / night shifts, which is easy to combine with day-time activities like studying or another job.
You are also taught interesting facts about the products you pick and help to sell to customers.
The pay is also alright for the time you work and you are provided free dinner if you work for the evening / night shift.
Svantaggi
Although your main priority is to pick orders that come in, they often want you to do other tasks like cleaning and checking dates on products. This is fine, but sometimes felt as the main task rather than secondary.
All coworkers are also of age or don't always speak your language, if you are young, you might feel out of place here.
Working during the day is also worse than the evenings / nights. As you are getting paid the same for more hours and will have to interact a lot more with customers. If this is what you like its fine, but else I would not recommend it.