From what I gather of what the original question is asking, I was thinking the same kinda thing. See, if you want to have a random level generator in a game, let's say it puts walls in random positions or adds powerups in random locations, etc, there might be some reason why you want to then later `keep` the way that level was set up so you can come back to it if it happened to be a good one. If you knew what seed the random numbers were based on you could have it then re-generate the same results later on using that same seed number. Then you could for example just save the seed number to refer to the layout of the level. In a lot of games you may want to have the player go back to a previously created `level` to replay it (although that slightly goes against the purpose of making levels randomly, it might be a good part of the game structure).
SSI had a dungeons and dragons gold box game like Hack or Moria... Thinking it was called Ulimited Adventures or something like that. I am almost sure it did exactly that. It seeded it's random number generator to create the dungeons. AND... It gave that number to the user. So if you wanted your friend to run through the exact same dungeon that you ran through, all you had to do was write down that "seed" and your friend could plop that number into his game and play the same dungeon. :)