You should know that formatting an SD card as internal storage is ideal for storing your applications, photos, videos and documents in. However, since it works as internal storage, your microSD card ...

Android phones have an in-built feature known as Adoptable Storage, which enables users to add an extra layer of storage space for music, pictures, videos, files, and so on.

If your Android phone is running out of storage space, many phones will allow you to insert an SD card, which you can set as the phone's primary storage.