We’d recommend only enabling the Jetpack features you want to use on your site.
Various features in Jetpack are actually designed to speed up your site by taking a load off your server – for example the following which are processed at Jetpack’s end:
– Site Accelerator – https://jetpack.com/support/site-accelerator/
– Stats – https://jetpack.com/support/wordpress-com-stats/
– Subscriptions – https://jetpack.com/support/subscriptions/
– Related Posts – https://jetpack.com/support/related-posts/
Similar features elsewhere traditionally make numerous requests to a site’s database.
There are also features such as Lazy Images – https://jetpack.com/support/lazy-images/ – specifically designed to speed up page load time.
That said, the more Jetpack features are enabled, the more processing your site (or in this case customers sites) would have to do, just as if you were adding separate plugins for those features. That’s why we always recommend enabling only the features needed.
In terms of speed and loading times, here’s an independent report that can shed more light on this in terms of Jetpack and it’s features: https://mattreport.com/jetpack-speed/
