In reply to Pooja.

Can you also address the concern of many bloggers that Jetpack slows down the blog or page? I think this will clear many doubts of the readers.

Hi! I work on the Jetpack team, and I'd like to offer some information that will hopefully address your concerns.

Jetpack is a big plugin. It offers a lot of features, and as a result I think it's only natural for folks to worry about the impact such a plugin could have on their site. It's definitely a great question to ask yourself when installing a new theme or plugin on your site. 👍

The good news is, that's something we in the Jetpack team take very seriously as well. In the past few years, we've continuously worked on improving the performance of every aspect of the plugin:

We update existing features to improve their performance.
We consider potential performance impacts whenever we develop and introduce new features.
Some of the features we add to the plugin are directly meant to improve performance on your site. Our image, file, and video CDNs are there to help, alongside features like Lazy Loading for your images for example.

In addition to the work we do within the plugin, we also rely on the WordPress.com cloud to improve your site's performance. When you install Jetpack, you connect your site to WordPress.com. Once you've done that, some of the Jetpack features you'll use will rely on the WordPress.com infrastructure. Instead of using your hosting plan's resources, the plugin will rely on WordPress.com to do some of the heavy lifting on your site. Things like backups will be stored safely on our servers; Related Posts will be indexed and processed on our servers instead of on yours. You can then choose to rely on those features instead of using a plugin that would do the work on your own site. This will have a positive impact on your site's performance.

All that said, some of the work will also fall on you. You will decide what Jetpack features you want to enable on your site, and you'll have to decide whether those features are worth the impact they may have on your site.
Let's look at some examples. Jetpack allows you to add several official sharing buttons at the bottom of all your posts, as well as widgets to display your latest Tweets, Instagram pictures, or posts on your Facebook Page. It also allows you to embed Instagram pictures or timelines within your posts, as discussed in the post above.
Each one of those things can be useful, but can also have an impact on your site's loading speed.
It's then up to you to decide whether you need all those sharing buttons, widgets, and embeds. You can give things a try, and adjust things as necessary.

I hope this clarified things a bit. If you ever have any questions or concerns about Jetpack, don't hesitate to reach out! We're always happy to answer any questions you may have about the service.