So, if you're a bit of an OCD person like me, you tend to not wait for the Play Store to send you notifications there are updates, you check it fairly regularly yourself.There's a new look now when you have the list of 'recently updated' apps. Either when it's time to update or the recently updated apps you'll see a little 'expand' v showing that if you tap it you'll get some more information.
That information it's showing is "what's new".
Before the update, if you wanted to find out what it was you were updating you'd have to click the app and be brought to the store's listing for it, scroll down and see.
(then there's the whole idea around how Google is the worst when it comes to listing what really is new)
I like this feature. The iOS App Store has had this for some time and it was one of the differentiators that I really liked.