How does the -seed thing work?

[Stolb3rg]

That isn't actually what it is supposed to do.
In 1.10 it now works properly, which is why you don't see it working buggedly like it did in 1.09.
It actually sets the game's global seed to a certain number (the one you type in as the parameter).  The game's random number generator creates each subsequent random number from the previous one, hence a "random stream".  By setting the seed, you will get the same random numbers for that game each time.
This is not to say the same things will happen, because the game generates random numbers all the time, and so if you do things in a different order you will use the same numbers at different times for different results.  Still, it is a generally non-sensible way to play if you are playing single player seriously.

Ok, Thanks but i dont know what you mean by numbers. The chances oif the item drops you mean? the place monsters are located?