There are very few moves in poker that are as powerful as the semi-bluff. It’s the one play that lets you bluff an opponent while still giving you some other ways to win in case he/she doesn’t fold. The idea is that you bet with a hand that’s decent but not great.
Usually a hand with some drawing potential. You’re OK with taking down the hand right then and there if your opponent folds. On the other hand if your opponent calls you might still be able to hit a powerful hand. If this happens you’re in a good position to win a potentially bigger pot because your opponent might be putting you on a straight-up bluff by this point.
It’s very easy to conceal your hand when you’re semi-bluffing. If the worst happens and you miss your outs than you can still fold without it being too much of an issue.