My experience? More often than not, the fee to hire an event consultant proves to be less expensive vs. the amount of money somebody/company would have unnecessarily spent without that industry expert guiding them. Maybe the company would have paid their keynote speaker more than the industry standard. Perhaps they know of a less expensive venue that would have worked just as well and what marketing is unnecessary. The list goes on.
Disclaimer: Numbers are my least favourite thing. But that's only because clients will often come to me with a set budget in mind, and people pleaser that I am, I'll stress out a bit when it's unrealistic and no avoiding the difficult explanation of why event breakdowns cost what they do. But there are ALWAYS opportunities to find the positivity of rethinking the budget in lieu of the original vision.