Is it OK to post the same content on each platform every day? Or should we post different updates on different sites?

In short: no. People follow your brand on different platforms for different reasons. This means that you can’t expect to have exactly the same audience across all platforms. That being said, unifying the audience is something you can achieve through storytelling. Brands focusing on visual content don’t necessarily have to rely only on one of the two platforms. Instead, they could start a story by posting the “making of” on Snapchat and the more polished photos on Instagram.