For the longest time Yahoo had stopped updating its desktop Messenger with the last update being March 2012 for Windows and July of that year for Mac OS X.
Since then, the company has focused more on its mobile client given that’s the way online-based communication was heading at the time—if you exclude services like Skype.
With the updated Yahoo Messenger for mobile dropping last December, some holdouts to the messenger have been calling for updates to fix problems and features that it should have by now had it continued to be updated. There were some plugins made for features such as group viewing of YouTube videos—which eventually became pointless thanks to YouTube group viewing services.
The new desktop Messenger for Windows is exactly the same as the mobile Messenger. You still can’t tell if your contacts are online or not, only essential features are here—pictures, emoticons, gifs from Tumblr. If you want the other features such as camera, you’ll want to stick with the original Messenger, but it will be ended by the end of August.