It is recommended to make an nandroid backup before changing system partition files.
Updating a system app decreases phone internal storage, because the update is stored in /data/app and the original apk is still in /system/app.
System app cleaner will automatically:
- backup the original apk in /sdcard/system cleaner/ (in case you want to restore the original apk)
- delete the apk in /system/app
- move the updated apk to /system/apk
- delete dalvik-cache(optional but recommended)
- reboot device (optional but recommended)
By doing this, a considerable amount of internal storage will be freed.