Earlier quoted context omitted.
Right, it's a deduction, not a credit, so it only partially pays for itself on a direct tax basis, but generally the expense is money the business would have spent anyways on its business. But the point is that a business with a higher tax rate has a greater incentive to spend money, and to spend more of it. And as a practical matter, history has demonstrated that businesses actually invest less during periods of low…
We haven’t seen a protracted low tax period under modern economic circumstances. Certainly considered in isolation this investment sounds attractive. In conjunction with the benefits of paychecks and dividends being spent elsewhere in the economy it’s less certain.
Changing personal income tax rates has a lagging effect on economic spending, because they're spread out over time so that effect ends up being very small on a monthly or bimonthly basis (i.e., the periods over which a person generally receives a paycheck). Generally, consumers don't even notice the change until the file the taxes for the year.
Businesses have had low taxes since the Reagan administration, albeit brief periods of higher taxes during the Clinton and Obama administrations. Notably, business investment was at its highest levels during those periods of high taxes, and the economy grew at its highest rates since the post-WWII reconstruction era. During the periods of low taxes, US businesses actually accelerated off-shoring labor to foreign facilities, and the decline of Detroit and the Rust Belt can be directly correlated with the Reagan tax cuts.