I guess it depends on your job personally, how many shifts they give you and whether you believe that it is affecting your results in a bad way.
Job, even during year 12, can be really good to save money, get real life experience, socialisation, and to actually get away from the mindset of school for a bit and have that balance. You never know as well, depending on your job, you may want to have a gap year of full time work after school to save money and get experience.
Cons though is that it can be stressful during year 12, have an effect on your time management etc. Work can be really exhausting and can take away a lot of the physical and mental energy it takes to study.
My teacher's rule of thumb is that you should be working no longer than
15 hours per week. Particularly in exam or assignment time this amount should be reduced based on how well you can cope.
Main thing is think about the amount of hours and shifts you get and whether this will affect your schooling. Do you enjoy work, do you really need the money?
If yes, communication with your boss is really important especially during year 12 as your availabilities are going to fluctuate - at the end of the day they are always going to find someone to cover for you.
Personally, I am keeping my casual job, I really enjoy what I do and the people I am surrounded with. The main thing for me is making sure my boss knows that I cannot work more than 15 hours per week and none at all during exams. If you get called in to work, you are allowed to say no! At the start of my job, this was so so hard for me to do, but at the end of the day, you are the one taking the exams and you need to set time for yourself for your studies.
I hope this helps and good luck in making your decision