Assuming the server seed commitment is known before placing a bet, the server can't alter the outcome in any way. Is is the idea that a server could predict betting patterns for an individual user (and shuffle cards / pick numbers accordingly)? That's the only thing I could think of which a client seed does prevent.
Yes, gamblers tend to be very predictable in their bets. If the gambler has the opportunity to add unique random data to the calculation of the result, the casino cannot predict the outcome of the bet ahead of time.
I see, so my assumption was correct. I just wanted to make sure it didn't serve some other purpose I hadn't thought of.
I am actually developing a multi party provably fair scheme (e.g. multiple players betting on the same "roll")
There is something similar to what you describe, see
https://www.bustabit.com/play The server seed is committed to before any player starts gambling, and cannot be changed, so the casino cannot change the server seed based on betting patterns. There are multiple players betting on the same roll, however each player is betting against the house; this prevents a sockpuppet player beating the other players with inside information.
@ pooya87 - your proposed solution will not be provably fair, and is described in the OP's
other thread. In your example, if Alice is a sockpuppet of the casino, it could wait until Bob reveals his seed based if the three combined seeds are a winning hand for the casino.