Pros
Good exposure to different writing styles/ magazines of different audiences. You're involved in all stages of the editorial/publishing process; I even once went with a supervisor for a visit to the printing press. My supervisors were open, communicative, supportive and sharp; they encouraged us to explore our own ideas and even let us write/design for the magazines. Solid mentorship.
Kontras
Your workload depends on the amount of staff. When I was an intern the team was unlucky enough to face two staff departure (one didn't pass probation, the other was moving to another company). We still supported each other well, but I could tell my supervisors got a little stressed because of their workload increase. Power to them for getting the magazines published still.