"Suitedness is extremely important. Some people underestimate how important it is for unpaired hands to be suited."
-Ed Miller, Playing the Player
Back when I was a newbie learning limit poker, I read in a variety of books, and was told numerous times by who I thought were knowledgeable players, that "suitedness" was not that important. In fact, I was frequently told--by otherwise expert players--not to treat suited cards any differently preflop than non-suited cards. "It only adds a few small percentage points to your equity" and "three to four percent is nothing" and "a couple percentage points is in the noise, and no one's good enough to realize the difference in their results" and even "low suited cards just get you into trouble; they're absolutely not worth the extra few percentage points" were all things I was advised.
Uh, wrong. Suitedness matters. Or, said more accurately, expected value matters.
Let's look at a simpleminded (but real world) example to illustrate. Imagine you've got Ace-Queen offsuit (AQo) on the button in a $1/2 NL full-ring cash game. A very tight player immediately to your right (in the cut-off seat) is playing a standard shove-or-fold short stack strategy. When the action folds to him, he open shoves all-in for $35. The action is on you. You look left, and notice that both blinds are probably going to fold. Should you call that shove or not??
For arguments sake, let's assume the villain is playing a solid, profitable shorty strategy, which means he's shoving with ~12% of his range here. This is 22+,ATs+,KQs,ATo+,KQo, which is pretty standard for this type of short-stack grinder.
At first glance, AQo looks pretty strong against this range, right? Wrong. It's actually a slight equity dog if you run the numbers: our 49.4% vs. villain's 50.6%. If we ignore the blinds and rake (which essentially cancel each other out), calling a $35 shove results in a loss of $0.42.
While forty-two cents doesn't sound like much, if you repeat it just 100 times, you'll end up a net loser for $42. Or $420 over 1,000 trials. Or $4,200 over 10,000 trials.... In other words, yes, you should actually fold your AQo. Yes, fold.
Now, in contrast, let's look at the same scenario, but this time we have suited AQ. Our equity against villain's range indeed only increases "a few small percentage points." In this case, however, those few percentage points turns us from a dog into an EV winner: our 51.9% vs. villain's 48.1%,. Said another way, we now realize a expectation of $1.33 per hand. Or about $133 over the 100 samples. Or $1,330 over 1,000 samples. Or $13,300 over 10,000 hands.... In other words, yes, you should call with AQs in this scenario, but fold the offsuit hand. Those few small percentage points actually matter. A lot.
Cash game poker is all about equity and EV. If you get your money in good--and you're properly bankrolled to ride out the variance swings--you will make money at the game. If you don't... well, you won't. End of story.
A lot of so-called experts aren't always so expert when it comes to the actual nuts and bolts of no-limit hold'em, especially if they learned by trial and error or never bothered to work out the math. Like the hippies of a previous generation might advise a poker player: Question authority. Or as a past anti-hippy President once famously said, "Trust, but verify."
All-in for now...
PS. While it ain't a particularly inexpensive book, I've found Ed Miller's Playing the Player to be a truly excellent read and chock-full of really good advice.