There’s a difference between a tax deduction and a tax credit. Let’s say, for the sake of simplicity, that the tax rate is 25%. If I spend 10 billion dollars on something, and it’s tax deductable, that means that I subtract 10 billion dollars from my income before I calculate my taxes, and therefore, the deduction ends up saving me 2.5 billion in taxes (25% of the 10 billion). By contrast, if there’s a 10 billion dollar tax credit for something, that means that after I calculate my tax burden as a percentage of my income, I can then subtract that credit straight off the amount I owe. So if I get a 10 billion dollar tax credit, that means that I pay 10 billion less in taxes. But tax deductions are far, far more common than tax credits.
Another implication of this is that it never makes sense to do something purely just to get a tax deduction from it. If whatever it is has some other benefits too, then the deduction might move it from the “not worth it” category to “worth it”, but only if there are those other benefits. For instance, all else being equal, a company that doesn’t make charitable donations will net more profit than one that does (of course, all else isn’t equal, and a company may well get other benefits from donations, such as better public relations or a better-prepared workforce).