When you use spread sheets a lot, much of what makes you productive is that you know exactly what Excel will do. Like yes I know it's going to try to increment when actually I want to fill this column with 1s or whatever, but I can hold ctrl and override it and all is good.

With copilot, you will never be sure what it's going to do. I feel like it would slow me down even if it guessed right 90% of the time.

I'm pretty sure it just replaces itself with what it thinks is the correct Excel expression. That way the use can audit and correct the AI's work (and Microsoft isn't liable for miscalculations). Firing off to co-pilot every evaluation would be insanely irresponsible.