Is there a policy that defines it? Is there a limit?
Would love to hear your experience as I'm doing some research into this right now.
Younger employees (college hire to 3 years or so) tend to be hired locally, with increasing levels of work-from-home allowed as time goes on, but we're flexible from day 1 in terms of "work from home to let in the plumber" type stuff. Generally, after a few months, we'll allow regularly scheduled work-from-home for "I need T/Th to do day care runs" stuff. And several a year go full-time remote, usually to flee DC real estate prices and traffic.
Mid-career employees, we'll hire remote from day 1.
With 1/3 of my product's staff in Bangalore, we have to be good at remote work anyway, so there's little, if any, cost to allowing US-based employees to work wherever they want.
Our HQ is outside DC and most new hires (at least one my product) are local. But, we have great flexibility - we can work from home on demand from day 1. And we regularly let employees go permanently remote when their personal situations change.
Prospective employees are always glad to hear that's one of the perks working here. Especially those that come from government contracts, where being on-site with a client is generally preferred, if not required.