They could also provide him with advice. Since they were smart witches and wizards, they might have knowledge and wisdom to pass on. Maybe they could guide Harry on how to deal with Voldemort or how to navigate the complex world of Hogwarts politics through the portraits.
The portraits could be a link to his family history. Harry has always been curious about his parents. Having their portraits could allow him to learn more about their lives, their friends, and the things they cared about. This knowledge could in turn help him better understand his own identity and his place in the wizarding world.
The portraits could offer him emotional support. Just seeing his parents' faces might give Harry the strength to face difficulties. For example, when he's feeling down or facing a tough decision, looking at the portraits could be like getting a warm hug from his parents, even if they're not physically there.