Comfrey cuttings into plants must be one of the easiest ways to feed your garden.
If nature didn't make it, someone would have invented it.

Dig out root, break into 2 inch pieces, plant horizontally, cover with compost, water well and leave it alone.

Some say better to dig up in Autumn, but I've dug it up and planted at all times of the year, without issue.

Leaves can be added to water-butt, stirred and (a bit smelly) but break down nicely to provide watering feed (1 to 100 parts water)
Leaves and stems can be cut, left to dry out for a day where potatoes are being planted, covered with compost and feeds well.
Leaves and stems can be cut and laid as mulch around tomatoes/potato plants, providing good feed.
Flowers are a great attraction to bees and other pollinators.
Slugs I've found, are not a fan of comfrey.

Don't buy it!
It can grow in dry and wet conditions, have a look around ponds, etc.
(I've seen comfrey cuttings advertised for £5/£6 - it's readily available for free, naturally)

If watering veg is a problem, then it's a great way to feed.
Some cut leaves and shred them into a drainpipe with some broken stones, so rain water runs through the pipe and into water butt, I've always added leaves directly to water butt.

It's also great for keeping down wild grass as it provides ground cover (ideal for around a pond) and helps prevention of ponds that dry out, where frogs hang out.

The comfrey roots deep, drawing minerals from as deep as 5 foot down, bringing it to the surface in it's leaves, which can provide natural food for plants.