Connecting your site to your WordPress.com account won’t create any new site on WordPress.com. It won’t change your site URL either.
It will only add a new menu with options under Jetpack > Settings, where you will be able to configure and turn options on and off on your site.
Connecting your site to a WordPress.com account basically means that you open a communication channel between your site and WordPress.com. You can then use this communication channel by turning on specific modules under Jetpack > Settings.
For example, if you were to turn on the Subscriptions module, your site would then use the communication channel to notify WordPress.com every time you publish a new post. Once we get notified, we would then send notification emails to your subscribers for you, from WordPress.com.
Can the plugin and all its resulting change be undone by uninstalling it, in case something went wrong or the plugin changed anything I didn’t want?
Yes. Like with any other plugin, you can deactivate it at any time by going to the Plugins menu in your dashboard. Once a plugin is deactivated, it doesn’t run on your site anymore.
Are they cons about this plugin? Like, would it be better for some types of persons or blog to avoid it?
When you open that communication channel I talked about earlier, it means that a third-party service, WordPress.com, starts having access to some of your site data. That means that your commenters’ email addresses will also be stored on WordPress.com, for example. If you use the Stats module, that means that your stats will be stored on WordPress.com. If you’re not comfortable with that, or if your site deals with private data that shouldn’t be shared with any third-party, Jetpack is probably not the plugin for you.
I hope this clarifies things a bit. Let me know if you have more questions!
