In simple terms, tax system encourages, actively, accumulation of leverage risks on companies capital accounts. Not only that, tax preferences for debt imply distorted U-shaped relationship between credit ratings (credit risk profile of the company) and the cost of capital, whereby top-rated A+, A and A- have higher cost of capital (due to greater exposure to equity) than more risky BBB and BBB- corporates (who have higher share of tax0deductible debt in total capital structure).
Which brings us to one benefit of reducing tax shield value of debt (either by lowering corporate tax rate, which automatically lowers the value of tax shield) or by dropping tax deduction on debt (or both). Here is a chart showing that when tax deductibility of debt is eliminated, companies with lowest risk profile (A+ rated) enjoy lowest cost of capital. As it should be, were risk playing more significant role in determining the cost of company funding, instead of a tax shield.