Changelog Issue – Oembed Twitter

you added Twitter oembed?
What does this mean? Twitter embedding is already in WordPress.
Does this new feature change anything?

WordPress itself does indeed handle Twitter oEmbeds. Jetpack adds an extra layer to some of the default oEmbed codes to allow you to use shortcodes to add tweets to your posts, and customize the look of these tweets. You can read more about it here:
http://en.support.wordpress.com/widgets/twitter-timeline-widget/#embedding-with-a-shortcode

But if you were using oEmbed on your site before, no worries: you can continue to use it, nothing will change!