Google often uses the Chrome beta for introducing more underlying features aimed at developers, as well as new features for the stable version that need testing before they actually make their way into the stable version used by the public. For example, Google brought in a new security panel for developers back in the Chrome 48 beta, and Chrome 49 beta is aiming to bring in more developer-focused tools and functions. For end users, the more interesting version of Chrome will be the upcoming Chrome 50 which is set to introduce a bunch of material design UI styling, and although it isn't officially available in Chrome just yet, you can actually check it out as of now.
As for the Chrome 49 beta, things like improved background sync will be introduced into the mix which will allow websites and developers to schedule a sync for anything that happens on a web page that a user might be browsing until the next time an internet connection becomes available. As Google notes in their example, if a user sends off an email and then leaves the page before the notification that the email has been sent pops up, chances are that the email would be lost, causing the user to have to resend the email. The improved background sync API is going to improve network reliability so these things shouldn't be as much of an issue.