That's not actually true. For instance our yearly debt used to be £60m per year up to around 2010, the benefit of reducing the tax bill is far outweighed by actually paying the debt. Corporation tax is at around 18% - let's say 20% - to actually have the tax bill outweigh that £60m yearly debt you'd have to be making £300m profit to begin with - in which case you have no real need for such a large debt.
Leveraged buy-outs, and high levels of leverage, are the bread and butter of hedge funds, you get to buy an asset using said asset as collateral, and then hopefully you can increase cash-flow, profits, and as a result net value. It doesn't always work though - Terra Firma's buyout of EMI for example, and also their purchase of the Four Seasons care homes operator more recently.
Leveraged buy-outs work - up to the point they're detrimental on the business growing due to the oversized debt. It's worked out for the Glazers.
But it's not for every business. If you have cash flow the way United do, you don't really need a large debt. The only use of that debt to begin with wad for the Glazers to purchase United - because they didn't have $800m in cash / assets to elsewise purchase us. We'd be far better off not having that debt to begin with - to the tune of almost $1b.
There are plenty of business that operate well debt-free. Though it's becoming more fashionable to take out debt due to the inflationary pressure on money today / low interest rates / qe, but that's a separate topic.