Most states it's legal to record audio without consent if you're a party to the conversation, and it's legal federally. Recording video in public is ok most everywhere.
For me personally I went to jail for false accusations of assault. I had no choice but to interact with a very scheming and hostile individual for a long time and if I'd not recorded the conversations - on advice from my friend and attorney - I'd have likely not beat the charges. So yeah... I very much have a scenario in mind where these would have been helpful and there are certainly others who can probably relate.