ive done it a number of times, including for my trial. in some ways it was an advantage and in smoe ways a dissadvantage.
the advantage was that after a 4hour shift coming home i felt prtty tired. Because they were exams they started a bit later than normal so i got like 9 hours sleep and felt fantastic for those exams.
the downside is you have less time to cram and prepare the night before. the truth is that no1 is ever completely prepared as well as t hey could be and those exstra few hours could have helped. All in all though, working shows what type of person you are to future employees and/or university interviewers.
it comes down to working is your choice and it probably wont affect you all that much