I always change names (except my husband's, because he doesn't mind) but also details that might make them recognisable. There has been a case where a fiction writer got in trouble for creating a character that was a bit too close to her real life neighbour. Even though it was fiction and she'd changed the name, it was still obvious who the character was based on. I also use a pen name if I think the person I'm writing about would be too recognisable in a situation under my real name.