If somebody chooses your career then you might not like the job and you might want to follow your dreams and do what you like to do. You may also not be very well with the job they give you.
If somebody picked a job for you it might be a good paying job. Also when somebody would give you a job you wouldn't have to worry about being jobless because they would give you a job.
It might be good if you had a job for a 12 year old then you could have money but then the job might be too hard for a 12 year old and they should also enjoy more of their childhood. You could help your parents with things that they need to pay