I used to practice in bare feet as a student. It is nice but I like the leverage and protection a good shoe provides. Sometimes a pedal will flip up suddenly and you can really hurt your feet with that. Some harpists have broken toes while pedaling.
Also I agree with the other posts. Sometimes if the harpist is a jazzer and therefore out of the normal realm not wearing shoes can be acceptable to the audience but for classical harpists it’s kind of strange (too informal) and also moving pedals with barefeet has a weird tendency to make the feet look really dexterous and wide at the same time, sort of a monkey with huge feet so unless you want to look like that shoes might be a good decision. Take a look at a lot of musician pictures where it was fashionable not to wear shoes. Once in a while the people can pull it off and it looks cool but most of the time it just looks weird.