What features are you using that the $18/user/month plan doesn't cover?

I don't pay for slack any more, I just picked the price of their enterprise plan. Large users probably get big discounts but it doesn't matter, the cutoff where this makes sense financially is probably around 4000 employees even at $10/seat

The article mentions some sort of legal audit reasons that the author is of the opinion that any reasonably sized company needs. These features are apparently only on the expensive plan.