interest expense is beneficial for?

I have a hard time wrapping my head around the benefit of interest's tax-deductibility. I understand that debt, up to a certain limit, can be beneficial for the WACC. However, comparing profits (NI) with and without the existence of interest expenses, I'd rather take more profits even if they were preceeded by higher taxes. But is taking the view of an eqity investor, i.e. comparing NI with and without interest expenses, actually the wrong approach and I should look at it from the perspective of all investors?

Does the benefit insted refer to EBIT - Taxes, which would be the company's profits to all investors?