I spoke to a director friend of mine a few years back about shooting in 4K. He says that when he works (whenever budget allows), he would always shoot in 5K, not because he wanted the extra resolution for the full frame but because he wanted the ability to crop the shot down without losing resolution. Some shots would be scaled down from 5K to 4K, but others would be cropped to 'zoom in', or allow for minor panning that wasn't present in the original camera work.
8K presumably provides the same benefits but to a greater scale; you can scale it down to 4K, you can 'zoom in' on parts of the shot (such as a subtle detail, a pickpocket stealing a wallet for example) without having to use a second camera or record the shot twice, and so on.
My phone (google pixel) does something like this for it's image stabilization.
When you film in 1080p it's actually a bit more zoomed in than you are expecting because it's really using the whole 4k+ sensor and applying some fancy coding to that to pan and zoom around in that space to provide some stability.
8K presumably provides the same benefits but to a greater scale; you can scale it down to 4K, you can 'zoom in' on parts of the shot (such as a subtle detail, a pickpocket stealing a wallet for example) without having to use a second camera or record the shot twice, and so on.