Building a Big Pot
The benefit of a big pot is that you can make big bets. Betting $500 into a $25 pot makes little sense. One of your opponents has to pick up queens, kings or aces only slightly more than one time out of twenty for this play to be unprofitable.
If you are making this play with queens, kings or aces, you are wasting a great hand. On the other hand, betting $500 into a $500 pot makes perfect sense. This is why you will build the pot with incremental bets over the early streets.
When a Big Pot Helps You
A big pot helps you when you have a very strong hand and are trying to win as much as possible, when you are trying to bluff, or when you are trying to give a draw bad odds to call.
Big Hand
Obviously if you are confident you have a hand that will win at showdown, you would like to bet as much as you reasonably can on the river. The bigger the pot, the easier this will be.
Big Bluff
Similarly, it's easier to run a big bluff at a big pot. If there is $50 in the pot, a bet of $200 or more is ridiculous and one much less than that may not scare anybody. If there is already $300 in the pot, you can make a scary $300 and potentially get someone off a hand.
Facing a Big Draw
Finally, if someone is drawing against you, the bigger the pot is, the more you can bet and get the opponent to call you with bad odds. If the pot is $100, it is a mistake for an opponent to call more than $25 with a flush draw with one card to come. You can probably get an opponent to make a bad $25 or even $50 call, but it would be nice to charge them more.
If the pot is $500, you can charge them $300. It's a bad call and high positive expectation for you, but very difficult for the opponent to fold.
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