I heard that a C-Corp being a one person shop (no other employees but the owner) can pay for the full amount 100% of personal rent if the residence is being used as a home office.
Sure. Especially if you don't mind being audited. Technically, it doesn't matter how the money gets where it goes as long as the income tax filings accurately describe the tax situation. But the IRS hates it when you make personal expenses from a business account, even if you've paid the required personal income tax (because their computers simply aren't smart enough to keep up with that level of chaos).
Also, on a non-tax level, commingling of business and personal funds can reduce the effectiveness of your company's liability protection and you could more easily become personally liable if the company goes bankrupt.
From what I understand the 30% would be the expense, and the 70% profit distribution.
I recommend you just pay yourself and pay the rent from your personal account and claim the allowed deductions properly like everyone else.
Why & when it would make sense to do this? Are there any tax benefits?
Never, because, no. You would still have to pay personal income tax on your 70% share of the rent (the 30% you may be able to get deductions for but the rules are quite complicated and you should never just estimate).
The only way to get money out of a corporation without paying personal income tax is by having a qualified dividend. That's quite complicated - your accounting has to be clear that the money being issued as a qualified dividend came from an economic profit, not from a paper profit resulting from the fact that you worked hard without paying yourself market value.