Many people talk about varying the way you play so that opponents will have a more difficult time determining what hands you might have. In actuality, it is usually impossible, or at least very difficult, to determine exactly which cards your opponents are holding. In practice you narrow their hands down to a range of hands, ie. they would push all in with AA or KK, so their range is those two hands. Widening your hand range, or at least being perceived to do so can have important benefits. In the above example, you would be right to fold KK vs. an opponent whose range is AA or KK only, but would be right to call if that person widened their range to include QQ or AK. So if I perceive that you would push all in with AK (when in reality you wouldn’t), you are causing me to make a significant mistake.
There is usually a fine line between costing yourself too much expected value in the present term in order to expand your range to gain yourself more expected value in the long term. I see far too many players against whom it is difficult to narrow down their range, but because their range is so wide, solid play defeats them. For example, if someone pushed all in every hand, they would be unreadable and their hand range would be wide, but it would be very easy to beat an opponent who plays like that.
Let me show you two examples where narrow hand ranges played a role in allowing me to win a pot I would not have ordinarily won.
Playing $5/$10 No limit with $2500 effective stacks.
There are 5 limpers and I call out of the small blind with 98o. The flop comes Jh7s5s giving me an open ended straight draw. I check, the big blind, who is a solid regular bets $50. 3 players call and I call as well. The turn is the Tc. I lead out $175 and the big blind makes it $675. Everyone else folds and I am 100% sure that he has the straight here. Because he is limited to only having the nut straight here (he wouldn’t raise 2 pair with so many people to act behind him, and wouldn’t bet the flop with 43 into so many people) we are currently splitting the pot. However, I can make it look like I have something else so that if a scary card comes on the river, I can bet and hopefully win the pot. Note how his limited range should allow me to play perfectly against him, while he has a more difficult time playing against me.
I elect to call and the best card comes on the river, the Js, bringing in the flush draw and pairing the board. I elect to shove all in and he grumbles about it being the worst card for the straight and folds. If he had a wider range then just the nuts on the turn(or if I thought he might have a wider range), then I would not have been able to play optimally against him and would have just shoved all in on the turn to with the hopes that he would call with a worse hand, or fold his equity in the pot.
Another example comes from pot limit omaha(in this game you MUST play 2 cards from your hand). Effective stacks are $700.
There are 2 limpers and I complete the small blind with 8c7c7s6s. The flop comes Jc9d7d. I bet $20 and only the big blind calls. I have played with him a bunch and know that he will only put a lot of money in with the nuts and will not be tricky.
The turn is a 4c giving me a flush draw along with bottom set. I bet $60 and the big blind calls. My plan is to bet a river that does not pair the board or complete a flush just in case he has a bigger set. Since I am representing T8 for the straight(and can easily have it), and I know he will never call the turn with the nuts or call the river without it, my bet is what I call a freeroll. I am rarely beat by a better hand, but just in case I am, I will win the pot anyways.
The river is the 2s, completing no draws. I bet the pot and the villain throws up his hands in disgust, shows me JJQT which had me in very bad shape, and folds it. If my opponent was tricky in this situation and could have just called with the nuts on the turn so that HE could win the pot if the board changed, then I would have had a lot more concern about betting the river(and the turn too). In this case, my opponents straightforward play caused him to lose a pot that another opponent might have won.