Both methodsBluetoothAdapter.startLeScan and BluetoothAdapter.stopLeScan were deprecated in Android Lollipop. As a replacement BluetoothLeScanner were introduced and acting as a scan controller.
If you develop BLE-based application you should control either scan via the BluetoothAdapter (Android 4.3 and Android 4.4) or the BluetoothLeScanner. The API introduced in Android Lollipop offers much greater features in terms of battery power consumption.