Google did not like external storage accessories such as SD cards. You can’t install applications on external microSD card. However, things changed after Android 6.0 Marshmallow. Yup, Android 6.0 introduces the ability to adopt external storage media to act like internal storage. Applications and data can be stored at external storage from now on. External storage media is formatted and encrypted when adopted. And can work with a single Android device at a time only. So it is safe to store both apps and private data for all users.