The way provably fair works is that setting your client seed is what determines every bet you will make with that seed, because each roll is server seed + client seed + nonce (the nonce is adding a sequential numbers to the end).  Adding a number to the client seed makes the roll change randomly.  From when you first set your client seed, the server can determine what your next 1 billion rolls would be if they wanted to.  They cannot however, change or manipulate these rolls.

If you feel you are unlucky, changing the client seed will change the outcome of your future rolls, so some people choose to do that because it makes them feel better, but statistically it provides no advantage.  It just gives you a different set of future rolls.