The big change is that Hangouts is being separated from Google Plus. Google mentions,
We want to highlight the following functionality currently present in classic Google+ that will not be available once Google+ becomes a core service:Will this have a huge impact on your daily use (or not) of Google PLus? Probably not. But fore-warned is fore-armed.
- Creating Events (users will still be able to view and delete existing events).
- Initiating Hangouts chats from Google+ (users will still be able to use Hangouts through the Hangouts app, on Gmail, or at hangouts.google.com).
- Using or creating Hangouts on Air (HOA) from Google+.
Note: users will still be able to create new live streaming sessions using YouTube Live. Users will also still be able to view and delete existing HOA data.
Read more here if you are interested in the nitty-gritty details.
Have a great day!