This site is under construction and is both very incomplete and subject to change.
The current cannonical site for documentation is here.

Why would I share any data with the developer of the plugin or theme I’m using?

By sharing your data with the developer or company behind the plugin or theme you’re using, you give them an opportunity to meet your unique needs in a better way. Using Freemius, our partners are able to spend more time focusing on their products and thereby offer better features for your website, and the decisions they make about their business are based on the data you are willing to share as a consumer.

They can also use the data to help make their businesses more sustainable by figuring out the best pricing strategies that work for customers like you and their businesses, which offers you long-term support and reliability for your plugin or theme purchase.