It doesn't matter if you're playing cash games or tournaments - the size of your stack dictates the style of play that is most profitable to you.
When you have a big stack you have freedom; when your stack is small you may only have one option.
What might be correct with a huge stack can be completely wrong when you're playing with a small stack.
And your optimum play is entirely different depending on whether your stack is 10, 50 or 300BBs.
Good Cash-Game Players Maximize Money on Table
In cash games, the max buy-in is often set. It can be 100BB, 200BB or even unlimited. If you ever lose a hand, you can always buy in back to the max.
Good players maximize their edge by having the most money on the table they possibly can. As a good player you should always be keeping close to the max buy-in on the table.
The reason for this should be obvious: money is a just a tool to extract chips from the other players.
The more money you have, the more money you can make from other players. If you hit the nut straight or a full house, you want to bet the maximum you can.
If you only have 30BBs on the table, you're losing value! So as a good player, always stay topped up.
Poker Tournaments are Different
In poker tournaments it's not quite the same.
Your stack is finite - you cannot buy back in. When you lose a pot you are stuck with what you have. When that's gone, you're out of the tournament.
Your chip stack is your life and you need to play the best poker you can with the chips you have.
Deep Stacks in Poker Mean Freedom
The deeper the stacks, the more freedom you have. Essentially when the stacks are deep (200BB+), pre-flop matters very little. The bulk of the betting happens on the later streets. You can play a much wider range pre-flop because the implied odds are so much greater.
The pre-flop hand values normalize and it becomes more of a post-flop chess game. Hands like suited connectors and all pocket pairs rise in value. When they hit, they make big pot hands (sets, flushes, full houses, etc.), whereas top-pair hands go down in value.
When top-pair hands hit, seldom do players want to put in a lot of money with deep stacks and one pair. One-pair hands win small pots often, and when they lose, they lose big.
How to Play a 100 Big Blind Stack
The normal stack is around 100 big blinds. This is what most online poker sites set their max buy-in to. 100BBs allows you some freedom, but you have to be more careful about your hand selection before the flop.
Most strategy books out there devote the bulk of their pages to playing this type of stack; to go into detail in a single article would be impossible.
For many strategy articles on playing 100BB stacks, take a look here.
How to Play a 35-50 Big Blind Stack
Medium stacks are between 35-50BBs. These stacks are what the bulk of most online tournaments are played at. At this level there is little room for pre-flop creativity. Hand selection is absolutely key. Since your stack is so small, you cannot rely on implied odds.
Drawing hands are pretty much thrown out the window. You're looking to play top-pair hands like A-K, A-Q, K-Q, etc., and big pocket pairs.
When they hit the flop they stand to be good a high percentage of the time. With a 35-50BB stack you maybe have a pre-flop raise, a flop bet and a turn bet in you.
Anytime you bet the flop and turn, your stack will be so small there will really be no (meaningful) river bet. So focus on hands that you can reliably get in on the flop.
How to Play a 15-35 Big Blind Stack
Small stacks are the bane of every cash-game pro's existence. Often these players will sit at the table and shove over every reraise until they double up or bust.
If it's the former, you can guarantee that this player will instantly sit out and move on to the next table to repeat as necessary.
But playing on the short stack, with 15-35BBs, is a facet of the game that needs to be mastered just like any aspect of poker ... especially if you plan on playing tournaments with any sort of frequency.
Despite the bad reputation that short-stackers have in cash games, it can be a very profitable style when played properly.
If the game is playing very aggressive before the flop, you can capitalize by buying in short and looking to get all-in before the flop or on the flop. Many players do not take short-stackers seriously, and will pay you off much more readily than if you had a larger stack.
Short-Stack Poker Strategy: Be Patient
The proper short-stack strategy is to be patient and wait for good top-pair hands and/or big pocket pairs. Suited connectors and small pocket pairs are meaningless to you.
You don't have nearly enough chips for a speculative hand to be of any value to you. Wait for one of these big hands and shove it pre-flop over an aggressive raiser, or wait until you connect with a flop and get it all-in.
With a stack this small you'll almost always be getting it in either pre-flop or on the flop, so concentrate on hands that figure to be best on the flop.
Drawing is a no-go. In tournament poker a 25-35BB stack is great for restealing.
When tournaments get to the late stages, players try and pad their stacks by stealing blinds. A 25BB stack makes for a great-sized stack for restealing.
If you notice players aggressively stealing blinds from late position, you can play back at them by reshoving your small stack over their pre-flop raise.
They will often be forced to fold their steals, winning you their raise as well as the blinds. This usually means a 4-6BB net gain for you!
How to Play a Tiny Stack
A tiny stack would be less than 15BBs. There's really no reason to ever play this short-stacked in a cash game. If you find yourself getting this low, either quit and buy yourself lunch, or rebuy.
If you're in a tournament, don't fret - many players have made comebacks with far less chips!
With 15BBs and less, it's time to go into push-or-fold mode. When you're this low you should be looking for first-in vigorish.
If the pot is folded to you you should be shoving with a fairly wide range - any ace, a good king, any pocket pair, big suited connectors, etc.
You need to build your stack by stealing the blinds and antes. Folding will only get you blinded out. There's no time to wait around for aces. Look for first-in vig and punish those blinds!
Always Be Aware of Your Stack Size
If you're playing cash, keep your stack topped up! Maximize your edge against worse players.
If you're playing tournament poker, remember that no matter what size your stack is, it has its pluses and its minuses.
Be aware of how each stack size should change your strategy. Adjust your style accordingly and you'll ultimately play better poker.