Jetpack comes bundled with a lot of useful features. For someone who is just starting out with WordPress, most of these features are a must have. They have a simple intuitive UI and are well integrated with other WordPress features.
The plugin is developed by Automatic, the same folks who created WordPress.com. So you can be sure that the plugin interacts seamlessly with your WordPress installation.
The only downside I see is these features come with only the very basic settings. As your site grows and your requirements evolve it may make more sense to switch to individual full-featured plugins.
Jetpack comes bundled with over 40 features. A few of these may be outdated or more suitable for specialized niches, so you just go ahead and deactivate those. But the rest of them provide important functionalities that should be utilized by any wordpress site.
Below I've compiled a list of the 15 most useful Jetpack plugins.
Display all your gallery photos in an immersive full screen carousel along with any comments & metadata.
This plugin enhances the WordPress comments by giving users an option to connect to their social media profiles while commenting. This makes the whole process much more faster and easier, and so more people would be willing to leave comments on your blog.
3. Contact Form
Contact forms are a great way to let your readers connect to you. This plugin lets you a add a fully customizable contact form to any post/page in just a few clicks. You can modify the form to choose your own custom fields.
4. Custom CSS
All themes may not provide all the options to customize the look and feel of your site. In these cases, you would either have to create a child theme or to change the source code itself and worry about it getting over written after every update. This plugin saves you the hassle by providing options to add your own CSS.
To use the plugin first activate it and then access it in Appearance -> Edit CSS.
5. Enhanced Distribution
If you enable this module, Jetpack automatically includes your content in WordPress.com Firehose. This is essentially a stream of all realtime wordpress content which is shared with third parties like Search Engines thereby increasing the reach of your post.
6. Extra Sidebar Widgets
This module provides various essential widgets that you can add to your website. It includes various widgets that allow readers to connect to your social media profiles and let you display images, galleries or top posts in your sidebar.
7. Mobile Theme
No matter what niche your blog is about, the majority of your readers will be accessing your blog on a small device. In a mobile first world, it is very important to make sure that your site works seamlessly on devices of all sizes.
There are various standalone plugins like WpTouch that let you make customizable mobile themes. But if you need something free & simple with the least work involved you should give the Jetpack mobile theme a try. All you need to do is activate the module and Jetpack automatically optimizes your site for the best experience on a small screen.
In my opinion, this is the most simple yet one of the most useful plugins in Jetpack. It pings your site every 5 minutes and notifies you if it is unreachable. It also lets you know as soon as it is back up along with the total downtime. This is one of the best ways to stay informed of any issues & to track the performance of your web hosting provider.
Photon is a CDN (Content Delivery Network) provided by Jetpack which serves all the images in your posts from WordPress.com network. Your images are cached in these CDNs, which are spread all across the world. This considerably speeds up your website and takes some load off your webserver.
Publicize make the job of managing your various social media profiles much more easier. You can configure it to automatically share your posts onto the connected social media sites. It currently supports Facebook, Twitter, Tumblr, Google+, Path & Linkedin.
11. Related Posts
This module shows related posts from your blog related to your article. The part that differentiates it from other similar plugins is that it takes the processing load for showing these posts off of your server. It utilizes the WordPress.com infrastructure for indexing and processing your posts.
This module provides you with configurable sharing buttons, that allow your readers to share your posts on various social media sites. It contains buttons for most major social networks and also allows you to add buttons manually for others.
13. Site Stats
There are many other more popular alternatives for getting Site Stats, but they generally tend to have a lot of information. It might be hard to understand all those numbers and graphs when you are just starting out. Jetpack provides an easy way to see the most significant numbers for your website in a nice graphic way without the added complexity. Even though I highly recommend having a fully featured analytics tool like Google Analytics set up for your website, but still having the additional Jetpack stats enabled helps you to get to the important stats faster.
This module provides you with a widget to let your users subscribe to your website. So every time you write a new post, your readers can get notified via email. Like most other Jetpack features, it takes the load of sending emails off of your web server. It also gives your readers the option to subscribe to comments, and to customize the emails being sent out.
15. Tiled Galleries
This module turns all your photo galleries into beautiful mosaics. You have a few different layouts to choose from. Also the photos are processed on WordPress.com servers so it doesn't put any extra load on your web servers. This feature may be just what you need to jazz up your website, without bloating it up too much with additional plugins.