I have an IO loan on a rental property. I find it useful to decide when I pay down principal (most months) and when I don’t want to (between tenants, months when the heater, dishwasher, etc are replaced).
I have found it to be extremely useful for cash flow purposes.
Again, this is a loan that is about 50% LTV and which I could theoretically pay off next month. However, that would require liquidating my money market (currently enough to cover 52 months of payments) and about 1/2 of my retirement assets (actually only need about 1/3, but would need to pay taxes and penalties so it goes up to about half).
