Pros
Friendly colleagues. On the weekends, most of the staff are young people (18-25years) which made working there feel like you were at school (in a good way!). Lots of opportunities to do overtime which is helpful if you are a student who needs extra cash in summer. Pay is pretty decent for a standard retail assistant position (£7.67 in London).
Cons
No staff benefits, except for 10% at christmas. Management can often treat you like you are a child (e.g. having to ask permission to use the toilet). There are so many employees, you often feel replaceable. Long queues means being on your feet for a long time. If you are contracted to work weekends, you must also work all bank holidays (boxing day, new years day, easter) and do not receive bonus salary for doing so (just standard hourly rate).