These two articles mention the fact that Facebook is comfortable with remote work, but might adjust salaries based on the actual location used for doing the work:
Facebook CEO Mark Zuckerberg said Thursday that most Facebook employees can work from home wherever they want. But they should not expect to get Silicon Valley salary levels if they relocate to less-expensive areas.
"We'll adjust salary to your location at that point," Zuckerberg said during a livestream, according to CNBC. "There'll be severe ramifications for people who are not honest about this."
The pandemics also created an opportunity for some those who can work 100% remote where I live (Eastern Europe), but I haven't heard of anyone adjusting the salaries due to working outside of a major city (metropolitan area).
I am wondering what is the rationale behind this. I am asking because this involves some costs (tracking your employees by location, possible demotivation due to salary reduction).
Question: What is the point of an employer to adjust the salary of an existing employer based on actual remote work location?
Note: This is very similar to this question, but the important difference is that here I am asking about existing employees.