i have a 128GB phone and just starts to use it, now it shows 30-40GB has already be used for system/user data. What kind of junks are installed? How do we clean them?
Samsung's OS OneUI has a pretty large footprint because they put a ton of features including stuff virtually nobody uses like Bixby. If you go into settings /Apps and then click show system apps you will see everything that's installed. If you click on an app name and the uninstall button isn't greyed out you can uninstall it. Samsung doesn't allow most of their programs to be uninstalled or disabled so you won't free much space.
On the plus side you can use an SD card for extra storage which isn't an option on most phones but you can't transfer apps to the SD card--it's pretty much just for documents, pictures, media files and backups.
Actually Samsung_BbvxxRb is misinforming you on both of his posts, you CAN move Apps to your micro SD card, and the extra Apps are called "bloatware" and can also be removed. To Move your Apps to your micro SD card (even the ones you THINK you cant): go into your system options (the cog icon that's in your notifications bar, scroll all the way to the bottom to about phone and press on it. Go down to "about phone" and go into that. Go down CV to "build number" and press on that 7 times. You will see a message pop up saying "developer options have been unlocked". Press back twice to go back out to the system options and you see "about phone" again and you will now see the newly unlocked "developer options" right next to about phone, go into the developer options, scroll all the way to the bottom until you see "force allow apps on external" and turn that on. Now go back to the options menu and go to "apps" under "apps" click on each app and scroll down to where it says "storage-internal storage and you will see "switch" press that and choose external. Bam, now your apps will be moved to external. Hope this helps.