Make sure that you’re only using the modules you want.
Most of Jetpack is designed to speed up your site by taking load off of your server, like our site accelerator https://jetpack.com/support/site-accelerator/ or stats https://jetpack.com/support/wordpress-com-stats/ subscriptions https://jetpack.com/support/subscriptions/ and related posts https://jetpack.com/support/related-posts/ which are all processed on our end (rather than hammering your database as these features traditionally do).
With that said though, the more Jetpack modules you add, the more your site has to initially process, just like it would if you added a separate plugin for the features, so always make sure you’re only using the features you want.
Regarding overall speed and load, here’s an excellent independent report: https://mattreport.com/jetpack-speed/
As for our Terms and Conditions, most all of Jetpack’s features make use of heavy processing power (our image CDN, related posts indexing), heavy database usage (stats), or require connections to third-party systems that can be very complicated to setup by yourself (Publicize’s automated sharing to social networks, email subscriptions, etc). We take care of that all on WordPress.com’s server cluster so your hosting provider doesn’t suspend you for using excessive resources.
In order to do any of that, we need to sync the data outlined at https://jetpack.com/support/what-data-does-jetpack-sync/ to our service, and we’re very upfront about that during the connection process prior to anything being synced.
Further details on that page outline what we sync, and of course we only sync data required for _active_ Jetpack modules, meaning that we only sync what we need to provide the features you want.
All synced data is handled under the terms of our Privacy Policy: https://automattic.com/privacy/
If you don’t want us to sync data to our service, we do recommend that you not use Jetpack, as it is integral to the services we offer.
Please let us know if you have any more questions!
