Heads up or "peeking" notifications, the little miniature pop-ups that appear in Android Lollipop if a notification comes in when you happen to be actually using your device, aren't for everyone. That's why Google will include the option to disable them on a per-app basis in the upcoming Android M release. (See Settings>Sound & Notification>App notifications in the Developer Preview.) It's also why apps like HeadsOff have sprung up to cater to those who want them to go away even sooner.