I remember when I went to music school in New Orleans, where I took a few guitar lessons with a well known jazz guitarist. He made me transcribe and learn this really difficult solo by Joe Pass.

I played it free hand for him, no anchor, in our next lesson together. He got on my case and said, "Man, you gotta anchor your hand for stability, this solo is hard". So I went home and relearned it with my hand anchored. It was a lot of work.

Then I got to our next lesson, and I played it for him with an anchored hand and he got on my case again and said "Man, you gotta play this free hand, you can't move freely with your hand all tied up like that, this piece is hard".

So there it is! My guitar teacher was contradicting himself, but I think he summed up the pros and cons quite nicely without intending to do so. Anchored hand feels secure, free hand gives you flexibility. With much more experience now, I only do free hand. If you do it enough, you get comfortable and secure with it so that you get the best of both worlds. Security comes from practice, and playing freely requires a flexible technique (which means no anchor). That would be my advice to anyone posing this question. I hope that's helpful.