Did you know that if you set the game to 1 winline instead of 10, you will most likely get 5 to 10 times higher game volatility? When you bet $2 on one line, your average win will be much higher (as less frequent) as when you bet $0.20 on 10 lines. When you bet on 10 lines at the same time, the wins in the paytable are 10 times smaller. In most slots you usually hit a winning combination only on a small number of the 10 lines, so your average wins are also lower.
Note that this trick usually cannot be used by high rollers, as the maximum bet per line is usually restricted. But there are also slots which are an exception. However, if you are a player who doesnot bet more than $2 in a single round, this trick is a must have.