This article about the iOS8 Message app has a lot of great insight about how one can improve a commonly-used feature , and the importance of attention to detail. The genius of this change is that they added an amazing amount of power, but what the user sees is not so different from iOS7 that they would get lost.
The only downside is that the change isn’t easy to discover for everyone. Tap and hold is pretty common now — he points out that many messaging apps like WhatsApp have it, and it’s something that Pinterest uses as well — but it’s not always clear in an interface what things support it.
These instantly sent pieces of media are also ephemeral. You have to explicitly ask to save them, or they self-destruct after 2 minutes.
tl;dr – if you tap and hold on the microphone or camera icon in your iMessage screen, you can send voice or pictures or video without launching another app. They’ve also made tapping on the camera icon show you the most recently taken photos so you can send them without searching. Easy-to-miss, but smart changes.