Quite a lot I think - setting your own hours, picking what you work on, picking who you work with, picking how you work (tools, meetings, 100% remote etc.), being able to work on side projects you can profit from without them being owned by your employer, potential to earn a lot more since you're working directly with clients, not having a boss to answer to (you have to answer to clients but not in the same way especially since you have multiple clients) and lots of freedom around vacations (which I'm guessing is closer to "unlimited vacations" than you'd get from an employer).

Unstable income, having to market yourself and more means it isn't for everyone though.

Not having to deal with the politics of the office or working with people you don’t like. Setting your own pay. I dunno, those seem like good ones to me.

Diversification. Personally speaking being accountable to a few customers has many mental benefits vs catering to the whims of a single boss.

Doesn't unlimited vacation just mean, take 3 weeks a year with your boss's permission if she/he gives it, or take a smaller bonus at the end of the year if you take more than your peers, or be shamed?

I've never heard anything about unlimited PTO that wasn't a riddle of caution and skepticism.

Paying lower taxes is generally another one. Employees generally can't deduct much.

Still offers greater upside on salary/income progression.

I make 3x as much as freelancer for the same work.