A wonder plant!  Comfrey is used widely by gardeners, food foresters and permaculturists, for good reason!  Its nutritious green tops make amazing compost tea or nutrient rich mulch.  It also makes very good, high value animal fodder, great for chooks.  The plant can act as a great barrier against grasses and can be used planted in a circle around fruit trees or boarding vege gardens etc.  Comfrey has deep tap roots, allowing it access to minerals that others struggle to reach.  It's this accumulation and sharing of minerals that makes comfrey such a great companion.  She gathers and shares minerals such as: silicon, calcium, potassium, phosphorus, iron, iodine and more!
 
Comfrey does not set viable seed, it is divisible by roots and will eventually form a large clump, so you do want to be mindful where you plant it.