Hello, there.
Jetpack does include quite a few features – Depending on the settings you’ve activated and the new elements you added to your site thanks to Jetpack, an impact on your site’s performance could be expected. For example, if you’ve added Like buttons, Related Posts, a few widgets, sharing buttons, and infinite scroll, that will indeed increase your site’s loading time.
I’m unsure how many you had active, but we would be happy to look at your site and see if we can find out clues as to what was happening here.
As with any other plugin, when enabling settings, the decision rests in which feature is worth the performance affect it could bring to your site. In general, any features that use images or call resources from third-party services (like the sharing buttons or the Facebook and Twitter widgets) will have an effect on your site speed.
If you ever feel that Jetpack features are making your site slower, but don’t know what particular feature is to blame, you can always log into your wp-admin dashboard and head to Jetpack > Settings and deactivate each module, one at a time, until you can pinpoint the performance dip on a specific module. You could then decide whether that feature is worth the impact it has on your site’s speed.
Another test that could really help (but one that should be done in off-peak times as far as your visitors are concerned) would be to deactivate all other plugins except for Jetpack to see if it truly is the cause for the load, or if another plugin is directly conflicting with Jetpack and causing load issues itself, triggering higher load for Jetpack functions to begin with.
If you decide to use Jetpack again, please let me know the results of this troubleshooting and we can go from there. Thanks!
