I get the idea...
The point of this is so you can get any old random seed and share it with your friends and have an adventure in the same world at different times. So one person could find a dungeon while someone else finds diamonds and then they tell each other about their finds. I know you don't have to have this, but this can allow you to share a world that isn't common such examples of easy to generate worlds: glacier, pig, creeper, chicken, and minecraft. Anything can be a seed but this makes a personal world that only you will know about.