The only thing I didn't like about the grocery warehouse and I'm not sure if all are like this but it wasn't paid hourly. It was piece-rate, which is great for the company but horrific for an employee.
Example:
We would come in the morning and have orders waiting to be picked. Once the orders are done, then we are done. If we picked slower, then we would be there 8 hours at $11 an hour because we were paid by the amount of pieces we pick an hour. If we picked faster then we could make $15 an hour but guess what? When everyone picks faster, the orders are done sooner. So $11 an hour X 8 hours = $88 in 8 hours vs $15 an hour X 6 hours = $90 in 6 hours.
In other words, only the company benefits by piece rate if the amount of work runs out. If you can't get your hours, working faster is pointlessly chasing your own tail.