Best of all, you can use it as an in-situ fertiliser. I plant a bunch of comfrey around each of my fruit trees, and then once or twice a year, I cut the leaves back and place them around the base of the tree. Chop ‘n’ drop mulching, no need to make compost.
Comfrey can self seed freely if there’s bare earth about the place, so best to use the sterile Russian Comfrey ‘Bocking 14’.
The Dwarf Comfrey Symphytum ibericum can be used in the same way, although it’s much lower and can be used as a ground cover plant.