I see people posting in threads, saying that 'anchoring will stop you progressing'. What is it? Because I want to know if I'm doing it because I feel like I'm in a rut.

There's a lot of different opinions on what anchoring is or isn't. But mostly it resting(or more forcefully anchoring) you're forearm on the top front of your guitar(like above the pickups bridge) - this will lead to less wrist movement across the string.

Others say resting your palm on the bridge(like palm muting) or "anchoring" your pinky below the pickups is bad. I sincerely don't think this is true. Especially if you happen to play shred or heavy music I believe it aids in your attack angle and speed. But again...a lot of people have different opinions.
Inflatable Guitar
Digitech GSP 2101/Mosvalve 962/Yamaha S412V
My Imagination