What is the appeal of prison planets?

Despite the really amazing waste of resources it would take to shoot people off into space to strand them on a prison planet, this trope has endured in SciFi literature and media through the decades. Sometimes the trope is used to provide an interesting setting as in the blockbuster movie Aliens3. Other times it is simply a small part of a larger story, as in Pitch Black and Chronicles of Riddick. It has shown up in episodes of popular TV shows, Like SG1, and even provided a plot twist for the TV series Earth2.

Every good SciFi trope needs a good what-if concept.
In these last two, there were no jailers or wardens, just “bad” people abandoned to fend for themselves. This version of the trope has a lot of good SciFi “what if” factor to it. What sort of society would evolve if a lot of bad people are left without good folk to guide them? Always interesting, but I’m still looking for a story like this done really well.

It helps to start with a plausible premise.
I’m currently reading Outcast Mine by Jamie Craig. In this story, the authors have done a good job of providing a plausible reason for the prison planet. The prisoners are being used as slave labor to mine a deadly and rare substance. Being exposed to the substance leads to a nasty death, so it makes sense that they would use the worst of the worst criminals to do this work. (Although, maybe if you’re advanced enough for space travel you might be able to come up with a robotic mining operation, but it is still good enough to suspend disbelief.)

Characters always make the story.
What really makes the book (at least so far) is the two central characters. First there is the human prisoner, Aleron, a charming rogue of a thief who ends up there by virtue of the fact that he’s escaped everywhere else. And the second character, Jasak, is the alien jailer whose mix of decency and hopelessness make him hugely sympathetic.  The twist here is that the jailers are also prisoners or outcasts from their home world. They keep the mine running and control the human prisoners in exchange for more privileges. I’m about three-fourths of the way through and there is an oddly sweet romance developing between this unlikely pair. Behind it all is a sinister plot about to unfold. So far, I’m rating this one high on my list for prison planet stories.

What do you think of the prison planet trope? Do you have a favorite story? Why do you think this trope is so enduring?