Look for bloatware in the dictionary

Hi there,

Just make sure that you’re only using the Jetpack modules you need. The more Jetpack modules you add, the more your site has to initially process, just like it would if you added a separate plugin. This can affect your site’s speed.

Having said that, most of Jetpack is designed to speed up your site by taking the load off of your server, like our site accelerator (https://jetpack.com/support/site-accelerator/) or the Stats (https://jetpack.com/support/wordpress-com-stats/) the Subscriptions (https://jetpack.com/support/subscriptions/) and the Related Posts (https://jetpack.com/support/related-posts/). All of these are processed on our end thus making your site faster.

Also, regarding Jetpack’s overall speed and load here’s an excellent independent report: https://mattreport.com/jetpack-speed/