There is a clear difference between land casinos and online rooms. The payout is the main difference, and the slots online can be as much as 20% greater than that of land based casinos.
The payout percentage is important for a machine, as it explains how much money of each turn is played back. For example, a player may wish to play some money. Keeping his winnings separately, he then takes the turns until his original pot is spent. He then looks at how much he has left, and calculates the percentage based on how many spins he has made. Quite often, the average payout of a machine is between 52% and 90% of each spin, and this is usually based on many spins. It is impossible to calculate the payout percentage of a machine after one or two turns, and it is therefore wise to continue playing over 100 turns before calculating.