> Somewhere else I remember reading this would also cut your salary by 10%.

It totally depends on where you're living. It could even be a salary increase if you were previously working in a lower CoL office but have since moved to a high CoL region -- in that case your salary would increase. There's definitely no blanket single figure that applies (in either direction) to people who go fully remote.

E.g. my grand-boss is a fully remote worker based out of Manhattan. He's getting the highest pay tier.