Google Hangouts has a feature not many users were even aware of, and now it's set to be discontinued. Said feature is SMS for Hangouts. Don't fret, though, as it's likely not what you think it is. Android users will still be able to send and receive text messages through the Hangouts app, and they will still be integrated into your regular Hangouts conversations.
The SMS for Hangouts feature just allowed users to get their Hangouts instant-messages sent them over SMS if they're in a location where they have cellular access, but no internet access. As you can imagine, this feature wasn't super popular (most users in this situation would just send and receive regular SMS texts anyway). Starting on July 2nd, that feature is going away.
Personally, I wasn't even aware of the 'SMS for Hangouts' feature, so to see it leaving the building means very little. Moreover, the feature likely had too few users to justify keeping it around, so I have my doubts that many people will be making too much of a fuss.
Of course, there's a chance you don't use Google Hangouts at all. Unless you have a Nexus or Google Play Edition Android phone, you already have a dedicated messaging application, even though you can integrate SMS into Hangouts. Plus, on non-Nexus or GPE phones, one needs to go out of their way to enable this feature.
The feature is set to be disabled tomorrow, leaving very little time for those who use it to find an alternative. If there is one, that is.