It's a difference in speed. I know people who can give an estimate of a scientific/technical idea working within about a minute by calculating things like signal strength by Fermi estimate.

It moves conversations along with a much better flow, because now you can focus on how to improve that, make a new estimate and iterate, and discuss the real-world implications from this, such as could you provide that much power or can you buy the components somewhere.

So, enough knowledge for Fermi estimates is really useful.