Answers from an Actual Lawyer
Note that this is general information, not legal advice, and does not form an attorney-client relationship. Please consult a specialized lawyer to address specific legal issues with respect to releases!
People, especially in certain states–like California and New York–have rights to their name, likeness, voice, and personal details. In many cases, even after they're dead! You, in having them on your podcast, are using some of their rights and distributing those out into the world–and that means you should have them signing a release. A release ensures that you have all of the rights that you need to do what you want with that content.
A release will generally outline that, in exchange for some type of compensation (monetary or otherwise, like publicity for them) or of their own free will (aka: for nothing at all), you get the right to use their voice and the info they’re going to share in the podcast. (This is the same reason that entertainment studios and record labels make people sign releases, even if that person is just going to be an extra in the background scene of a movie.)
While it may sound silly, some standard release language includes “throughout the universe and beyond” and “in perpetuity”–because one day there might be podcasts on Mars, and you want to make sure you have the rights to distribute your podcast to the Martian colonies, of course! (Fun fact: Not having broad language in content like this caused problems for some folks in the past that didn’t anticipate worldwide distribution or new media channels like iTunes.)
Releases don’t have to be involved or scary–we’re really talking about a couple of sentences. In most states, you can send your guest an email with the release language and have them write back and say “I agree.”
At the very least, if you’re worried about burdening your guest with a novel-length release, or the logistics of having your guests use DocuSign or HelloSign, or even if it’s just a spur-of-the-moment guest-spot, you can at least record at the beginning of your show you reading the release language and your guest agreeing before you proceed with the interview. Obviously, you’d edit that out of the publicly distributed episode, but you still have this person agreeing to your release in your records. It doesn’t have to be all legalese, either. You could say something like:
“Just a quick release: I want to make sure that I have your permission to use your name, likeness, and any info you share here. You understand that we’re going to share it so that listeners, potentially throughout the world, can hear it, and that we both agree that I’m the owner of all of the rights to this content. Sound good?”
A common pitfall that a release will help you avoid is an editing dispute. You may have a guest on your show who says something they think was stupid, didn’t put them in a flattering light, or that was confidential. You might feel like what they said is great scoop, and if you edited it out it would make the whole episode useless. In your release, you can specify if guests have “final cut” or “edit rights” and avoid the argument entirely.
Another pitfall is a dispute over usage rights. Imagine that the best episode you ever made was an interview with a famous painter–and then that painter dies! Suddenly, everyone wants to listen to your episode, and you’re approached about turning it into a TV show. Now, if you didn’t have the artist sign a release, it’s time to pump the breaks–it may not be clear if you have the right to their voice, name and personal information shared in your podcast after they die. If you do use their voice, surprise! Their family or estate may have a claim against you for any money that you make in connection with the use of that interview. So, even if you don’t anticipate a dispute with your guest in particular, a release is still a great idea.
Here’s some more info on releases and fair use.
Hungry for more info on podcasting legal issues? Check out previous Answers From an Actual Lawyer:
Do I need a co-host agreement?
Are my vendor agreements legit?
Do I need an LLC?