As Sally says, nettles are full of nutrition. We find our sheep don't eat them when they (the nettles) are young, but they eat them later in the year. Nettles are also the food plant of tortoiseshell butterfly larvae.
However, you can have too much of a good thing. We never spray chemicals, and where we have nettles we don't want, we mow them, with an ordinary lawn mower, frequently. If the problem is nettles under hedges and in awkward to reach places, as opposed to open pasture, then they are scythed as a temporary measure, but in the long term you can only wait for the tree cover to shade them out.
If, when you say 'on the plot' you mean a veg garden, then there's nothing you can do other than digging out every last root (they extend a long way, and are yellow ). Make sure you never let them seed, and hoe off any germinating seedlings before they get established. Don't put nettles on the compost heap unless you are sure they have not set seed. You can make a lovely, if decidedly stinky, liquid feed with a high nitrogen content, from soaked nettles - complements comfrey feed which is high in potassium.