Art for exposure, do or dont?

Spend your time on the internet searching for a job, and sooner rather than later you will come across an offer saying something along the lines of ‘Great exposure in exchange for your art, join us now!’ Or in other words, give us your time and effort for free, while drawing exactly what we want you to draw, and we make sure people see it.
This isn’t necessarily always a bad thing, but this completely depends on the context of it all. So what should you pay attention to? And when should or shouldn’t you do art for exposure? Here’s a little guide for you.