It kind of works if the tasks can be neatly packaged and handed off for totally asynchronous work. It breaks down as soon as you need the part-time person to work with the rest of the team.

You end up forcing the rest of the team to work around one person's schedule. You also end up with someone on your team doubling up on the part-time person's knowledge if you need someone available during normal hours to answer questions or debug something.

It's not really about benefits. ACA doesn't require full benefits for someone working 20 hours a week.

Let's be honest: Many remote work jobs are essentially becoming half-time jobs, with the other half of the work week comprised of simply being available on Slack if someone asks a question.