Storage Folders

Im switching over to a Galaxy S3 and was trying to move over some files and backups that I have made. Strange thing is that I couldn't find the file that was backing up my SMS/MMS messages. I knew the folder but couldn't locate it, it was looking for /mnt/sdcard. Only after enabling root access for ES File Explorer did I locate the folder. Thats when I started looking through the file structure and located three folders that look to contain that exact same thing, /storage/sdcard0/, /sdcard and /mnt/sdcard. My main concern is that these folders are taking up a lot of space that I shouldn't be using.