Sometimes you might you have a Monday to Friday job but you want to pick up another job for your spare Saturdays. Sometimes you might spend Monday to Friday on other pursuits or hobbies and you only want to work weekends. Either way, there are definitely some benefits to working on Saturdays. Firstly, if it's a casual position or there are penalty rates then you can look forward to making more cash than those who are only there on weekdays. It always feels better when you know you're working for a decent hourly rate.
Another benefit is that when you work on the weekend it can actually seem more exciting. Whether you work in hospitality and everyone is out and about enjoying themselves or you work in an office and it feels kind of special that there is hardly anyone there, there is definitely an extra element of excitement. Plus you get to feel good about being productive and working towards something while many other people are just lazing at home watching TV. If you're able to keep Sundays for yourself then you're only missing out on one day of the weekend anyway, which is not too bad at all.
Depending on the role you may need to step up on the weekend because you have less supervision. In this case you need to make sure you are not getting distracted and you're getting enough done that the boss will be happy with you. If you work somewhere that's actually busier on the weekends (like in hospitality), then you'll need to be prepared to work efficiently and effectively to get everything done! Either way, you'll need to be just diligent and hardworking as you would be on a weekday.