If you targeted APIs before Android 6.0 (e.g. you targeted API Level 21 - Lollipop), you didn't have to ask users for permissions to access contacts, sms, SD card and other data. Which made all the new security improvements in Android rather moot - scummy apps (like Snapchat :P) just didn't update their API levels, kept collecting personal data without asking for permission... AND didn't implement improvements of new OSes because they wanted to keep collecting data without restriction.
This is finally great news for Android security.