If you're developing Themes/Plugins and want to update them on various websites you own/manage, it can be quite a hassle.
One way would be to use WP Remote and bulk update all your plugins and themes.
This method assumes that all your plugins are on Wordpress.org, where most Plugins/Themes are.
The problem with that is that it's not always the case, you wouldn't want to submit your plugin to Wordpress.org if:

• You have a private premium plugin that a client bought (on a private repository on GitHub/Bitbucket)
• Most of your users are your own clients and you don't feel the need to publish your Plugin/Theme
• SVN, which is Wordpress.org's version control system, makes you feel like it's 2008 (can't blame you)

Another way would be to connect via FTP and overwrite all your plugins & themes.
This method takes too long, and is not always possible for some clients.

WP Pusher to the rescue!

WP Pusher lets you connect your GitHub/Bitbucket repositories as normal Plugins/Themes.
This is useful because you don't need to submit your plugins, make sure everything is synced between your websites, or anything like that.
It's important to mention that the Push-to-Deploy feature (that auto-updates on push) is not on the free plan.
The Pricing model is very affordable - You get unlimited Plugins/Themes for free (have to manual update those), for $39 you get the Push-to-Deploy feature and are allowed to use the plugin for Personal Use, and for $99 you can use it commercially.
Both paid plans include E-Mail Support + Updates for 1 year.

Seems like a solid automation tool, and a great idea in general.