The primary incentive that comes to mind is improved availability. Often, instances can become slow, so I use another. By hosting a local instance I could always have a smooth experience.
Scores are federated, resulting in a consistent global feed across instances and a lack of uniqueness for each instance. I wish hosting an instance provided a more customized experience like this. It would be a great incentive.
Every server that federated the post will retain a local copy of it that can be interacted with. The control over my data is mostly me having control of what info gets put out there about me personally and who can access my private data on lemmy