I read this story by Doyle Brunson, where he was talking about a guy he was playing with who started raising nearly every hand. By the time the rest of the players adjusted to him, he tightened back up and got his good hands paid off. Once they adjusted to how tight he was playing, he loosened up again and started bluffing down big pots. It made it very difficult for the sharks at the table. Afterwards, the player apologized to Doyle about how bad he was playing. Apparently, he had gotten into a fight with his wife and it was affecting his game. He'd get control every once in a while, but then would lose it again. He promised to never let it happen again. Doyle said the man was absolutely correct and that he never played good poker again.
The whole story was to illustrate the importance of switching gears. I got to thinking about it again, after some players were talking about the concept in a game I was in. Some of them felt there was no need to switch gears in a cash game, which I believe is 100% incorrect.
Now, switching gears should only be done once you're competent enough in your game to be able to play multiple styles. You should be able to play as either a loose-aggressive or a tight-aggressive at will, having entirely different hand ranges that you're able to deploy successfully. It would be a disaster to switch to a style you're not comfortable with, only to lose whatever profits you've made up to that point.
So the argument, that switching gears is unnecessary in a cash game, was that you should simply try to maximize your EV (expected value) in every hand you're in. Every move you make should have a mathematical justification. But poker is a metagame. You should be working to maximize your EV for the entire session, not just for an individual hand.
The real goal in No-Limit Hold'em is to get your opponent all-in when you have the best hand. Anything else, like winning small pots or bluffing down pots, should really just be to support & grow your stack while you look for the large takedown. They're all secondary consideration to getting your big hands paid off.
And no one is going to pay off your big hands unless they make a mistake. Most good players are not going to make that kind of mistake without some sort of provocation. That provocation needs to come in the form of playing an opposite style than they expect.
There are a couple gear changes that I think are essential in any cash game:
1.) Make large bluffs. You have to be willing to risk portions of your stack on a series of bluffs. If you win them, then great. Don't show your cards and keep it up. Exploit the overly tight play and let your stack keep growing. But you eventually want to get caught making a big bluff and have to show your cards when they call. You've now introduced some uncertainty. Your opponents won't feel comfortable folding as often and you will now hopefully get some of your big hands paid off.
2.) Allow yourself to be bluffed. I find that sometimes, with overly aggressive players, it's best to let them pull off a bluff. Especially in small to medium pots. This is even if I have a good read that I'm ahead in the hand. My goal is to make them feel so confident with their bluffing game that I can check-raise when we're involved in a large pot. Also, the optimal bluffing frequencies are actually much lower than most people realize. If you can spend the first half of your session convincing your opponents that they should bluff higher than that frequency, you can usually start picking them off in the last half.
I know those two concepts sound contradictory, since following through with your plan in #2 would make you vulnerable to plan #1. But the key here is that you want to make your opponents comfortable with sub-optimal play (and uncomfortable with optimal play). Changing gears is difficult and your opponents will usually stick to the same style if it seems to be working for them. Don't let them know it's a mistake until it's too late. And on the flip side, if they're playing optimal, you want them to think it's not working and get them started on the more difficult process of changing styles mid-game.
When you are with very good players, who can easily exploit whatever style you've adopted, changing gears becomes even more important. Whenever you change to a new style, there will be some lag before the good players have adjusted to it. The time during that lag is when you will win most of your money. Let them try to exploit you based on what style they think you're playing. But you should be exploiting them based on the style you're forcing them to use.