However, it is really the best interface I've found for setting a budget. Probably the best feature is that it can naturally incorporate overspending. If you set your grocery budget to $200 and you spend $250, YNAB isn't just like "yo, reduce your grocery spending." It remembers that you overspent by $50 and encourages you to incorporate that into next month's budget in a flexible way.
Unless you're a multimillionaire, you can probably benefit from using it. In fact, even if you are quite wealthy, plenty of celebrities have demonstrated repeatedly that it's still possible to go broke in just a few years.