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.
To me the only benefit in defederation is in blocking instances with illegal content. I would never use StackOverflow if there was a chance of not seeing the top answer to the questions I search.
most instances based in jurisdictions with rules similar to your own will do a good job on thier own policing and removing that content, the ones that don’t will be in hot water.
im more thinking of things that are often subjective and more marginal like the disposition of various levels of NSFW or other highly divisive content. On your own instance, for just you and yours, its less of an issue just removing what you dont want to see and as an admin the blocks are much more effective. If you are a big instance taking those stances becomes a big show every time and it can be why some instances my not or be slow to react to content on the margins.
For a personal instance, no one cares, its like you are blocking something in your personal email client.