Decrypter can save the files on your disk as an iso image, then burn it to the disk if it is already small enough to fit onto a dvdr. It is also one of the most recommended ways of burning to dual layer dvd's right now. To do this you change the mode to iso read, then iso write.
I've also found that Decrypter is better at ripping dvd's with scratches. Shrink can be a little fussy with imperfect disks. So, if you run into one that Shrink can't handle, its good to have Decrypter around.